A heat sink (or heatsink) is an environment or object that absorbs and dissipates heat from another object using thermal contact (either direct or radiant). Heat sinks are used in a wide range of applications wherever efficient heat dissipation is required; major examples include refrigeration, heat engines, cooling electronic devices and lasers.
Principle
Heat sinks function by efficiently transferring thermal energy ("heat") from an object at a relatively high temperature to a second object at a lower temperature with a much greater heat capacity. This rapid transfer of thermal energy quickly brings the first object into thermal equilibrium with the second, lowering the temperature of the first object, fulfilling the heat sink's role as a cooling device. Efficient function of a heat sink relies on rapid transfer of thermal energy from the first object to the heat sink, and the heat sink to the second object.
The most common design of a heat sink is a metal device with many fins. The high thermal conductivity of the metal combined with its large surface area due to the fins result in the rapid transfer of thermal energy to the surrounding, cooler, air. This cools the heat sink and whatever it is in direct thermal contact with. Use of fluids (for example coolants in refrigeration) and thermal interface material (in cooling electronic devices) ensures good transfer of thermal energy to the heat sink. Similarly a fan may improve the transfer of thermal energy from the heat sink to the air by moving cooler air between the fins.
Performance
Heat sink performance (including free convection, forced convection, liquid cooled, and any combination thereof) is a function of material, geometry, and overall surface heat transfer coefficient. Generally, forced convection heat sink thermal performance is improved by increasing the thermal conductivity of the heat sink materials, increasing the surface area (usually by adding extended surfaces, such as fins or foam metal) and by increasing the overall area heat transfer coefficient (usually by increase fluid velocity, such as adding fans, pumps, etc.).
Online heat sink calculators from companies such as Novel Concepts, Inc., can accurately estimate forced convection heat sink performance. For more complex heat sink geometries, and/or heat sinks with multiple materials, and/or heat sinks with multiple fluids, computation fluid dynamics (CFD) analysis is recommended (see graphics on this page).
Use in electronics
Explanation
In common use, it is a metal object brought into contact with an electronic component's hot surface — though in most cases, a thin thermal interface material mediates between the two surfaces. Microprocessors and power handling semiconductors are examples of electronics that need a heat sink to reduce their temperature through increased thermal mass and heat dissipation (primarily by conduction and convection and to a lesser extent by radiation). Heat sinks are widely used in electronics, and have become almost essential to modern integrated circuits like microprocessors, DSPs, GPUs, and more.
Construction and materials
A heat sink usually consists of a base with one or more flat surfaces and an array of comb or fin-like protrusions to increase the heat sink's surface area contacting the air, and thus increasing the heat dissipation rate. While a heat sink is a static object, a fan often aids a heat sink by providing increased airflow over the heat sink — thus maintaining a larger temperature gradient by replacing the warmed air more quickly than passive convection achieves alone — this is known as a forced air system.
Heat sinks are made from a good thermal conductor such as copper or aluminum alloy. Copper (401 W/(m·K) at 300 K) is significantly heavier and more expensive than aluminum (237 W/(m·K) at 300 K) but is also roughly twice as efficient as a thermal conductor. Aluminum has the significant advantage that it can be easily formed by extrusion, thus making complex cross-sections possible. The heat sink's contact surface (the base) must be flat and smooth to ensure the best thermal contact with the object needing cooling. Frequently, a thermally conductive grease is used to ensure optimal thermal contact; such grease usually contains ceramic materials such as beryllium oxide and aluminium nitride, but may alternatively contain finely divided metal particles, e.g. colloidal silver.[1] Further, a clamping mechanism, screws, or thermal adhesive hold the heat sink tightly onto the component to maximize thermal conductivity, but specifically without pressure that would crush the component.
PC marketplace
Due to recent technological developments and public interest, the retail heat sink market has reached an all time high. In the early 2000s, CPUs were produced that emitted more heat than ever before, escalating requirements for quality cooling systems.
Overclocking has always meant greater cooling needs, and the inherently hotter chips meant more concerns for the enthusiast. Efficient heat sinks are vital to overclocked computer systems because the higher a microprocessor's cooling rate, the faster the computer can operate without instability; generally, faster operation leads to higher performance. Many companies, including ThermalTake, Cooler Master, and Zalman, now compete to offer the best heat sinks for PC overclocking enthusiasts.
In soldering
Temporary heat sinks were sometimes used while soldering circuit boards, preventing excessive heat from damaging sensitive nearby electronics. In the simplest case, this means partially gripping a component using a heavy metal crocodile clip, hemostat or similar clamp. Modern semiconductor devices, which are designed to be assembled by reflow soldering, can usually tolerate soldering temperatures without damage. On the other hand, electrical components such as magnetic reed switches can malfunction if exposed to higher powered soldering irons, so this practice is still very much in use. [1]
Recent developments
More recently, synthetic diamond cooling sinks are being researched to provide better cooling. Also, some heat sinks are constructed of multiple materials with desirable characteristics, such as phase change materials, which can store a great deal of energy due to their heat of fusion.
[edit] As a problem in firestopping and fireproofing
Fire test where the steel pipe penetrants clearly act to absorb and conduct heat from the furnace, through to the unexposed side.
A heat sink is rarely a desired thing in passive fire protection. Rather, it is usually a problem that must be overcome to maintain fire-resistance ratings. The proven ability to overcome heat sinks in construction is subject to building code and fire code regulations.
[edit] Firestopping
Problem - Metallic penetrants and sleeves, at a density of 7.9 kg/L are denser than common firestops or concrete. Consequently, during a fire, they will absorb more photons and seek to conduct these to the unexposed side of a fire barrier (thus "cooling" the exposed side at the expense of the unexposed side), such as the cold side of a firewall. This is undesirable. Even if the fire is stopped by the barrier, one must keep the unexposed side cool to prevent autoignition of combustibles on the unexposed side of a fire barrier. The unexposed side may very well be an area of refuge, which must be safeguarded to comply with the building code. Greater penetrant and sleeve conductivity leads to lower T-ratings. Higher density firestops, such as firestop mortars act as a heat sink to absorb heat away from small penetrants, such as cables, thus increasing T-ratings.
Benefit - a rare exception where heat sinks are beneficial in firestops is where intumescents must be activated, such as in a firestop containing a plastic pipe. Heat sinks such as wire mesh and extra metallic sleeving may be used to carry heat to intumescents to activate expansion such as to choke off a melting plastic pipe or melting pipe covering, such as foamed plastic or fibreglass.
[edit] Fireproofing
In fireproofing of structural steel as well as providing circuit integrity to cables, cable trays, junction boxes and electrical conduit, the metallic items that are protected by the fireproofing measures act as a heat sink. Fireproofing methods are used to defeat the heat sink properties of the items they protect. In the case of circuit integrity measures, electrical services will fuse and short circuit above 140°C.
NOTE:
2008年10月28日星期二
Heat pipe
A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hotter and colder interfaces.
Inside a heat pipe, at the hot interface a fluid turns to vapour and the gas naturally flows and condenses on the cold interface. The liquid falls or is moved by capillary action back to the hot interface to evaporate again and repeat the cycle.
Structure, Design and Construction
Diagram showing components and mechanism for a heat pipe containing a wick
Cut-away view of a 500 µm thick flat heat pipe, with a thin planar capillary (aqua colored)
Thin flat heat pipe (heat spreader) with remote heat sink and fan
A typical heat pipe consists of a sealed pipe or tube made of a material with high thermal conductivity such as copper or aluminium. A vacuum pump is used to remove all air from the empty heat pipe, and then the pipe is filled with a fraction of a percent by volume of working fluid, (or coolant), chosen to match the operating temperature. Some example fluids are water, ethanol, acetone, sodium, or mercury. Due to the partial vacuum that is near or below the vapor pressure of the fluid, some of the fluid will be in the liquid phase and some will be in the gas phase.
Inside the pipe's walls, an optional wick structure exerts a capillary pressure on the liquid phase of the working fluid. This is typically a sintered metal powder or a series of grooves parallel to the pipe axis, but it may be any material capable of exerting capillary pressure on the condensed liquid to wick it back to the heated end. The heat pipe may not need a wick structure if gravity or some other source of acceleration is sufficient to overcome surface tension and cause the condensed liquid to flow back to the heated end.
A heat pipe is not a thermosiphon, because there is no siphon. Thermosiphons transfer heat by single-phase convection. (See also: Perkins Tube, after Jacob Perkins.)
Heat pipes contain no mechanical moving parts and typically require no maintenance, though non-condensing gases (that diffuse through the pipe's walls, result from breakdown of the working fluid, or exist as impurities in the materials) may eventually reduce the pipe's effectiveness at transferring heat. This is significant when the working fluid's vapour pressure is low.
The materials chosen depend on the temperature conditions in which the heat pipe must operate, with coolants ranging from liquid helium for extremely low temperature applications (2–4 K) to mercury (523–923 K) & sodium (873–1473 K) and even indium (2000–3000 K) for extremely high temperatures. The vast majority of heat pipes for low temperature applications use some combination of ammonia (213–373 K), alcohol (methanol (283–403 K) or ethanol (273–403 K)) or water (303–473 K) as working fluid.
The advantage of heat pipes is their great efficiency in transferring heat. They are a much better heat conductor than an equivalent cross-section of solid copper. A heat flux of more than 230 MW/m² has been recorded (nearly four times the heat flux at the surface of the sun).[1]
Heating a volatile liquid at a fixed volume can be dangerous, since the pressure can exceed the strength of the container (see pressure vessel). The pipe must safely withstand the pressure that occurs when all of the fluid is in the vapor phase at high temperature. Most importantly, the maximum pressure in the heat pipe must be limited by carefully restricting the total mass of working fluid.
Active control of heat flux can be effected by adding a variable volume liquid reservoir to the evaporator section. Variable conductance heat pipes employ a large reservoir of inert immiscible gas attached to the condensing section. Varying the gas reservoir pressure changes the volume of gas charged to the condenser which in turn limits the area available for vapor condensation. Thus a wider range of heat fluxes and temperature gradients can be accommodated with a single design.
A modified heat pipe with a reservoir having no capillary connection to the heat pipe wick at the evaporator end can also be used as a thermal diode. This heat pipe will transfer heat in one direction, acting as an insulator in the other.
Flat heat pipes
Thin planar heat pipes (heat spreaders) have the same primary components as tubular heat pipes. These components are a hermetically sealed hollow vessel, a working fluid, and a closed-loop capillary recirculation system.
Compared to a one-dimensional tubular heat pipe, the width of a two-dimensional heat pipe allows an adequate cross section for heat flow even with a very thin device. These thin planar heat pipes are finding their way into “height sensitive” applications, such as notebook computers, and surface mount circuit board cores. It is possible to produce flat heat pipes as thin as 0.5 mm (thinner than a credit card).
Heat transfer
Heat pipes employ evaporative cooling to transfer thermal energy from one point to another by the evaporation and condensation of a working fluid or coolant. Heat pipes rely on a temperature difference between the ends of the pipe, and cannot lower temperatures at either end beyond the ambient temperature (hence they tend to equalise the temperature within the pipe).
When one end of the heat pipe is heated the working fluid inside the pipe at that end evaporates and increases the vapour pressure inside the cavity of the heat pipe. The latent heat of evaporation absorbed by the vaporisation of the working fluid reduces the temperature at the hot end of the pipe.
The vapour pressure over the hot liquid working fluid at the hot end of the pipe is higher than the equilibrium vapour pressure over condensing working fluid at the cooler end of the pipe, and this pressure difference drives a rapid mass transfer to the condensing end where the excess vapour condenses, releases its latent heat, and warms the cool end of the pipe. Non-condensing gases (caused by contamination for instance) in the vapour impede the gas flow and reduce the effectiveness of the heat pipe, particularly at low temperatures, where vapour pressures are low. The velocity of molecules in a gas is approximately the speed of sound and in the absence of non condensing gases, this is the upper velocity with which they could travel in the heat pipe. In practice, the speed of the vapour through the heat pipe is dependent on the rate of condensation at the cold end.
The condensed working fluid then flows back to the hot end of the pipe. In the case of vertically-oriented heat pipes the fluid may be moved by the force of gravity. In the case of heat pipes containing wicks, the fluid is returned by capillary action.
When making heat pipes, there is no need to create a vacuum in the pipe. One simply boils the working fluid in the heat pipe until the resulting vapour has purged the non condensing gases from the pipe and then seals the end.
An interesting property of heat pipes is the temperature over which they are effective. Initially, it might be suspected that a water charged heat pipe would only work when the hot end reached the boiling point (100 °C) and steam was transferred to the cold end. However, the boiling point of water is dependent on absolute pressure inside the pipe. In an evacuated pipe, water will boil just slightly above its melting point (0 °C). The heat pipe will operate, therefore, when the hot end is just slightly warmer than the melting point of the working fluid. Similarly, a heat pipe with water as a working fluid can work well above the boiling point (100 °C), if the cold end is low enough in temperature to condense the fluid.
The main reason for the effectiveness of heat pipes is the evaporation and condensation of the working fluid. The heat of vaporization greatly exceeds the sensible heat capacity. Using water as an example, the energy needed to evaporate one gram of water is equivalent to the amount of energy needed to raise the temperature of that same gram of water by 540 °C (hypothetically, if the water was under extremely high pressure so it didn't vaporize or freeze over this temperature range). Almost all of that energy is rapidly transferred to the "cold" end when the fluid condenses there, making a very effective heat transfer system with no moving parts.
Origins and research in the United States
The general principle of heat pipes using gravity (commonly classified as two phase thermosiphons) dates back to the steam age. The modern concept for a capillary driven heat pipe was first suggested by R.S. Gaugler of General Motors in 1942 who patented the idea.[2]The benefits of employing capillary action were independently developed and first demonstrated by George Grover at Los Alamos National Laboratory in 1963 and subsequently published in the Journal of Applied Physics in 1964.[3] Grover noted in his notebook:"Heat transfer via capillary movement of fluids. The "pumping" action of surface tension forces may be sufficient to move liquids from a cold temperature zone to a high temperature zone (with subsequent return in vapor form using as the driving force, the difference in vapor pressure at the two temperatures) to be of interest in transferring heat from the hot to the cold zone. Such a closed system, requiring no external pumps, may be of particular interest in space reactors in moving heat from the reactor core to a radiating system. In the absence of gravity, the forces must only be such as to overcome the capillary and the drag of the returning vapor through its channels."
Between 1964 and 1966, RCA was the first corporation to undertake research and development of heat pipes for commercial applications (though their work was mostly funded by the US government). During the late 1960s NASA played a large role in heat pipe development by funding a significant amount of research on their applications and reliability in space flight following from Grover's suggestion. NASA’s attraction to heat pipe cooling systems was understandable given their low weight, high heat flux, and zero power draw. Their primary interest however was based on the fact that the system wouldn’t be adversely affected by operating in a zero gravity environment. The first application of heat pipes in the space program was in thermal equilibration of satellite transponders. As satellites orbit one side is exposed to the direct radiation of the sun while the opposite side is completely dark and exposed to the deep cold of outer space. This causes severe discrepancies in the temperature (and thus reliability and accuracy) of the transponders. The heat pipe cooling system designed for this purpose managed the high heat fluxes and demonstrated flawless operation with and without the influence of gravity. The developed cooling system was the first description and usage of variable conductance heat pipes to actively regulate heat flow or evaporator temperature.
Corporate R&D
Publications in 1967 and 1968 by Feldman, Eastman, & Katzoff first discussed applications of heat pipes to areas outside of government concern and that did not fall under the high temperature classification such as; air conditioning, engine cooling, and electronics cooling. These papers also made the first mentions of flexible, arterial, and flat plate heat pipes. 1969 publications introduced the concepts of the rotational heat pipe with its applications to turbine blade cooling and the first discussions of heat pipe applications to cryogenic processes.
Starting in the 1980s Sony began incorporating heat pipes into the cooling schemes for some of its commercial electronic products in place of both forced convection and passive finned heat sinks. Initially they were used in tuners & amplifiers, soon spreading to other high heat flux electronics applications. During the late 1990s increasingly hot microcomputer CPUs spurred a threefold increase in the number of U.S. heat pipe patent applications. As heat pipes transferred from a specialized industrial heat transfer component to a consumer commodity most development and production moved from the U.S. to Asia. Modern CPU heat pipes are typically made from copper and use water as the working fluid.
Applications
Alaska pipeline support legs cooled by heat pipes to keep permafrost frozen.
Grover and his colleagues were working on cooling systems for nuclear power cells for space craft, where extreme thermal conditions are found. Heat pipes have since been used extensively in spacecraft as a means for managing internal temperature conditions.
Heat pipes are extensively used in many modern computer systems, where increased power requirements and subsequent increases in heat emission have resulted in greater demands on cooling systems. Heat pipes are typically used to move heat away from components such as CPUs and GPUs to heat sinks where thermal energy may be dissipated into the environment.
Solar Thermal
Heat pipes are also being widely used in solar thermal water heating applications in combination with evacuated tube solar collector arrays. In these applications, distilled water is commonly used as the heat transfer fluid inside a sealed length of copper tubing that is located within an evacuated glass tube and oriented towards the sun.
In solar thermal water heating applications, an evacuated tube collector can deliver up to 40% more efficiency compared to more traditional "flat plate" solar water heaters. Evacuated tube collectors eliminate the need for anti-freeze additives to be added as the vacuum helps prevent heat loss. These types of solar thermal water heaters are frost protected down to more than -3 °C and are being used in Antarctica to heat water.
Pipelines over permafrost
Heat pipes are used to dissipate heat on the Trans-Alaska Pipeline System. Heat produced by friction and turbulence in the moving oil would conduct down the pipe's support legs and melt the permafrost which anchors them. Heat pipes with radiators at the top are used on each leg to keep them cold so they won't melt the permafrost and let the pipeline collapse.
Limitations
Heat pipes must be tuned to particular cooling conditions. The choice of pipe material, size and coolant all have an effect on the optimal temperatures in which heat pipes work.
When heated above a certain temperature, all of the working fluid in the heat pipe will vaporize and the condensation process will cease to occur; in such conditions, the heat pipe's thermal conductivity is effectively reduced to the heat conduction properties of its solid metal casing alone. As most heat pipes are constructed of copper (a metal with high heat conductivity), an overheated heatpipe will generally continue to conduct heat at around 1/80 of the original conductivity.
In addition, below a certain temperature, the working fluid will not undergo phase change, and the thermal conductivity will be reduced to that of the solid metal casing. One of the key criteria for the selection of a working fluid is the desired operational temperature range of the application. The lower temperature limit typically occurs a few degrees above the freezing point of the working fluid.
NOTE:
Inside a heat pipe, at the hot interface a fluid turns to vapour and the gas naturally flows and condenses on the cold interface. The liquid falls or is moved by capillary action back to the hot interface to evaporate again and repeat the cycle.
Structure, Design and Construction
Diagram showing components and mechanism for a heat pipe containing a wick
Cut-away view of a 500 µm thick flat heat pipe, with a thin planar capillary (aqua colored)
Thin flat heat pipe (heat spreader) with remote heat sink and fan
A typical heat pipe consists of a sealed pipe or tube made of a material with high thermal conductivity such as copper or aluminium. A vacuum pump is used to remove all air from the empty heat pipe, and then the pipe is filled with a fraction of a percent by volume of working fluid, (or coolant), chosen to match the operating temperature. Some example fluids are water, ethanol, acetone, sodium, or mercury. Due to the partial vacuum that is near or below the vapor pressure of the fluid, some of the fluid will be in the liquid phase and some will be in the gas phase.
Inside the pipe's walls, an optional wick structure exerts a capillary pressure on the liquid phase of the working fluid. This is typically a sintered metal powder or a series of grooves parallel to the pipe axis, but it may be any material capable of exerting capillary pressure on the condensed liquid to wick it back to the heated end. The heat pipe may not need a wick structure if gravity or some other source of acceleration is sufficient to overcome surface tension and cause the condensed liquid to flow back to the heated end.
A heat pipe is not a thermosiphon, because there is no siphon. Thermosiphons transfer heat by single-phase convection. (See also: Perkins Tube, after Jacob Perkins.)
Heat pipes contain no mechanical moving parts and typically require no maintenance, though non-condensing gases (that diffuse through the pipe's walls, result from breakdown of the working fluid, or exist as impurities in the materials) may eventually reduce the pipe's effectiveness at transferring heat. This is significant when the working fluid's vapour pressure is low.
The materials chosen depend on the temperature conditions in which the heat pipe must operate, with coolants ranging from liquid helium for extremely low temperature applications (2–4 K) to mercury (523–923 K) & sodium (873–1473 K) and even indium (2000–3000 K) for extremely high temperatures. The vast majority of heat pipes for low temperature applications use some combination of ammonia (213–373 K), alcohol (methanol (283–403 K) or ethanol (273–403 K)) or water (303–473 K) as working fluid.
The advantage of heat pipes is their great efficiency in transferring heat. They are a much better heat conductor than an equivalent cross-section of solid copper. A heat flux of more than 230 MW/m² has been recorded (nearly four times the heat flux at the surface of the sun).[1]
Heating a volatile liquid at a fixed volume can be dangerous, since the pressure can exceed the strength of the container (see pressure vessel). The pipe must safely withstand the pressure that occurs when all of the fluid is in the vapor phase at high temperature. Most importantly, the maximum pressure in the heat pipe must be limited by carefully restricting the total mass of working fluid.
Active control of heat flux can be effected by adding a variable volume liquid reservoir to the evaporator section. Variable conductance heat pipes employ a large reservoir of inert immiscible gas attached to the condensing section. Varying the gas reservoir pressure changes the volume of gas charged to the condenser which in turn limits the area available for vapor condensation. Thus a wider range of heat fluxes and temperature gradients can be accommodated with a single design.
A modified heat pipe with a reservoir having no capillary connection to the heat pipe wick at the evaporator end can also be used as a thermal diode. This heat pipe will transfer heat in one direction, acting as an insulator in the other.
Flat heat pipes
Thin planar heat pipes (heat spreaders) have the same primary components as tubular heat pipes. These components are a hermetically sealed hollow vessel, a working fluid, and a closed-loop capillary recirculation system.
Compared to a one-dimensional tubular heat pipe, the width of a two-dimensional heat pipe allows an adequate cross section for heat flow even with a very thin device. These thin planar heat pipes are finding their way into “height sensitive” applications, such as notebook computers, and surface mount circuit board cores. It is possible to produce flat heat pipes as thin as 0.5 mm (thinner than a credit card).
Heat transfer
Heat pipes employ evaporative cooling to transfer thermal energy from one point to another by the evaporation and condensation of a working fluid or coolant. Heat pipes rely on a temperature difference between the ends of the pipe, and cannot lower temperatures at either end beyond the ambient temperature (hence they tend to equalise the temperature within the pipe).
When one end of the heat pipe is heated the working fluid inside the pipe at that end evaporates and increases the vapour pressure inside the cavity of the heat pipe. The latent heat of evaporation absorbed by the vaporisation of the working fluid reduces the temperature at the hot end of the pipe.
The vapour pressure over the hot liquid working fluid at the hot end of the pipe is higher than the equilibrium vapour pressure over condensing working fluid at the cooler end of the pipe, and this pressure difference drives a rapid mass transfer to the condensing end where the excess vapour condenses, releases its latent heat, and warms the cool end of the pipe. Non-condensing gases (caused by contamination for instance) in the vapour impede the gas flow and reduce the effectiveness of the heat pipe, particularly at low temperatures, where vapour pressures are low. The velocity of molecules in a gas is approximately the speed of sound and in the absence of non condensing gases, this is the upper velocity with which they could travel in the heat pipe. In practice, the speed of the vapour through the heat pipe is dependent on the rate of condensation at the cold end.
The condensed working fluid then flows back to the hot end of the pipe. In the case of vertically-oriented heat pipes the fluid may be moved by the force of gravity. In the case of heat pipes containing wicks, the fluid is returned by capillary action.
When making heat pipes, there is no need to create a vacuum in the pipe. One simply boils the working fluid in the heat pipe until the resulting vapour has purged the non condensing gases from the pipe and then seals the end.
An interesting property of heat pipes is the temperature over which they are effective. Initially, it might be suspected that a water charged heat pipe would only work when the hot end reached the boiling point (100 °C) and steam was transferred to the cold end. However, the boiling point of water is dependent on absolute pressure inside the pipe. In an evacuated pipe, water will boil just slightly above its melting point (0 °C). The heat pipe will operate, therefore, when the hot end is just slightly warmer than the melting point of the working fluid. Similarly, a heat pipe with water as a working fluid can work well above the boiling point (100 °C), if the cold end is low enough in temperature to condense the fluid.
The main reason for the effectiveness of heat pipes is the evaporation and condensation of the working fluid. The heat of vaporization greatly exceeds the sensible heat capacity. Using water as an example, the energy needed to evaporate one gram of water is equivalent to the amount of energy needed to raise the temperature of that same gram of water by 540 °C (hypothetically, if the water was under extremely high pressure so it didn't vaporize or freeze over this temperature range). Almost all of that energy is rapidly transferred to the "cold" end when the fluid condenses there, making a very effective heat transfer system with no moving parts.
Origins and research in the United States
The general principle of heat pipes using gravity (commonly classified as two phase thermosiphons) dates back to the steam age. The modern concept for a capillary driven heat pipe was first suggested by R.S. Gaugler of General Motors in 1942 who patented the idea.[2]The benefits of employing capillary action were independently developed and first demonstrated by George Grover at Los Alamos National Laboratory in 1963 and subsequently published in the Journal of Applied Physics in 1964.[3] Grover noted in his notebook:"Heat transfer via capillary movement of fluids. The "pumping" action of surface tension forces may be sufficient to move liquids from a cold temperature zone to a high temperature zone (with subsequent return in vapor form using as the driving force, the difference in vapor pressure at the two temperatures) to be of interest in transferring heat from the hot to the cold zone. Such a closed system, requiring no external pumps, may be of particular interest in space reactors in moving heat from the reactor core to a radiating system. In the absence of gravity, the forces must only be such as to overcome the capillary and the drag of the returning vapor through its channels."
Between 1964 and 1966, RCA was the first corporation to undertake research and development of heat pipes for commercial applications (though their work was mostly funded by the US government). During the late 1960s NASA played a large role in heat pipe development by funding a significant amount of research on their applications and reliability in space flight following from Grover's suggestion. NASA’s attraction to heat pipe cooling systems was understandable given their low weight, high heat flux, and zero power draw. Their primary interest however was based on the fact that the system wouldn’t be adversely affected by operating in a zero gravity environment. The first application of heat pipes in the space program was in thermal equilibration of satellite transponders. As satellites orbit one side is exposed to the direct radiation of the sun while the opposite side is completely dark and exposed to the deep cold of outer space. This causes severe discrepancies in the temperature (and thus reliability and accuracy) of the transponders. The heat pipe cooling system designed for this purpose managed the high heat fluxes and demonstrated flawless operation with and without the influence of gravity. The developed cooling system was the first description and usage of variable conductance heat pipes to actively regulate heat flow or evaporator temperature.
Corporate R&D
Publications in 1967 and 1968 by Feldman, Eastman, & Katzoff first discussed applications of heat pipes to areas outside of government concern and that did not fall under the high temperature classification such as; air conditioning, engine cooling, and electronics cooling. These papers also made the first mentions of flexible, arterial, and flat plate heat pipes. 1969 publications introduced the concepts of the rotational heat pipe with its applications to turbine blade cooling and the first discussions of heat pipe applications to cryogenic processes.
Starting in the 1980s Sony began incorporating heat pipes into the cooling schemes for some of its commercial electronic products in place of both forced convection and passive finned heat sinks. Initially they were used in tuners & amplifiers, soon spreading to other high heat flux electronics applications. During the late 1990s increasingly hot microcomputer CPUs spurred a threefold increase in the number of U.S. heat pipe patent applications. As heat pipes transferred from a specialized industrial heat transfer component to a consumer commodity most development and production moved from the U.S. to Asia. Modern CPU heat pipes are typically made from copper and use water as the working fluid.
Applications
Alaska pipeline support legs cooled by heat pipes to keep permafrost frozen.
Grover and his colleagues were working on cooling systems for nuclear power cells for space craft, where extreme thermal conditions are found. Heat pipes have since been used extensively in spacecraft as a means for managing internal temperature conditions.
Heat pipes are extensively used in many modern computer systems, where increased power requirements and subsequent increases in heat emission have resulted in greater demands on cooling systems. Heat pipes are typically used to move heat away from components such as CPUs and GPUs to heat sinks where thermal energy may be dissipated into the environment.
Solar Thermal
Heat pipes are also being widely used in solar thermal water heating applications in combination with evacuated tube solar collector arrays. In these applications, distilled water is commonly used as the heat transfer fluid inside a sealed length of copper tubing that is located within an evacuated glass tube and oriented towards the sun.
In solar thermal water heating applications, an evacuated tube collector can deliver up to 40% more efficiency compared to more traditional "flat plate" solar water heaters. Evacuated tube collectors eliminate the need for anti-freeze additives to be added as the vacuum helps prevent heat loss. These types of solar thermal water heaters are frost protected down to more than -3 °C and are being used in Antarctica to heat water.
Pipelines over permafrost
Heat pipes are used to dissipate heat on the Trans-Alaska Pipeline System. Heat produced by friction and turbulence in the moving oil would conduct down the pipe's support legs and melt the permafrost which anchors them. Heat pipes with radiators at the top are used on each leg to keep them cold so they won't melt the permafrost and let the pipeline collapse.
Limitations
Heat pipes must be tuned to particular cooling conditions. The choice of pipe material, size and coolant all have an effect on the optimal temperatures in which heat pipes work.
When heated above a certain temperature, all of the working fluid in the heat pipe will vaporize and the condensation process will cease to occur; in such conditions, the heat pipe's thermal conductivity is effectively reduced to the heat conduction properties of its solid metal casing alone. As most heat pipes are constructed of copper (a metal with high heat conductivity), an overheated heatpipe will generally continue to conduct heat at around 1/80 of the original conductivity.
In addition, below a certain temperature, the working fluid will not undergo phase change, and the thermal conductivity will be reduced to that of the solid metal casing. One of the key criteria for the selection of a working fluid is the desired operational temperature range of the application. The lower temperature limit typically occurs a few degrees above the freezing point of the working fluid.
NOTE:
electrical electronic components
CPU shim
A CPU shim (also called CPU spacer) is a shim used between the CPU and the heat sink in a computer. Shims make it easier and less risky to mount a heatsink on the processor because it stabilizes the heatsink, preventing accidental damaging of the fragile CPU packaging. They help distribute weight evenly over the surface.
CPU shims are usually made of thin and very flat aluminium or copper. Copper has good heat dissipation capacity but is electrically conductive. CPU shims should be non-conductive to prevent any accidental short circuiting. Aluminium shims are often anodized, which makes them non-conductive and improves their appearance (see case modding). It is also very important that the shim is the proper thickness. If it is too thick then the heatsink will not make contact with the CPU, resulting in poor cooling and possibly overheating.
Most shims are CNC manufactured, often using laser cutting. Cheaper ones may be pressed or stamped which could make them less accurate.
They can usually be bought for less than USD$10.
Usage
CPU shims are not common at all in OEM computers, but are used by some computer hardware enthusiasts who may use heavier heatsinks because they wish to have a cooler or less noisy system or perhaps to overclock the CPU for better performance. A heavy heatsink puts more pressure on the CPU and motherboard. Shims are very useful for people who often change CPU, heatsink and/or cooling solutions, or use a heatsink that is heavier than the CPU manufacturer's recommended weight.
CPU shims are nowadays largely obsolete because most modern processors designed for home users since the introduction of the Athlon 64 and Pentium 4 have Integrated Heat Spreaders (IHS) which prevents the CPU core from getting accidentally broken.
NOTE:
Computer cooling
Computer cooling is the process of removing heat from computer components.
An OEM AMD heatsink mounted on to a motherboard.
A computer system's components produce large amounts of heat during operation, including integrated circuits such as CPUs, chipset and graphics cards, along with hard drives. This heat must be dissipated in order to keep these components within their safe operating temperatures, and both manufacturing methods and additional parts are used to keep the heat at a safe level. This is done mainly using heat sinks to increase the surface area which dissipates heat, fans to speed up the exchange of air heated by the computer parts for cooler ambient air, and in some cases softcooling, the throttling of computer parts in order to decrease heat generation.
Overheated parts generally exhibit a shorter maximum life-span and may give sporadic problems resulting in system freezes or crashes.
//
Causes of heat build up
The amount of heat generated by an integrated circuit (e.g., a CPU or GPU), the prime cause of heat build up in modern computers, is a function of the efficiency of its design, the technology used in its construction and the frequency and voltage at which it operates.
The dust on the laptop CPU heat sink after three years of use has made the laptop unusable due to frequent thermal shutdowns.
In operation, the temperature levels of a computer's components will rise until the temperature gradient between the computer parts and their surroundings is such that the rate at which heat is lost to the surroundings is equal to the rate at which heat is being produced by the electronic component, and thus the temperature of the component reaches equilibrium.
For reliable operation, the equilibrium temperature must be sufficiently low for the structure of the computer's circuits to survive.
Additionally, the normal operation of cooling methods can be hindered by other causes, such as:
Dust acting as a thermal insulator and impeding airflow, thereby reducing heat sink and fan performance.
Poor airflow including turbulence due to friction against impeding components, or improper orientation of fans, can reduce the amount of air flowing through a case and even create localised whirlpools of hot air in the case.
Poor heat transfer due to a lack or poor application of thermal compounds.
Damage prevention
It is common practice to include thermal sensors in the design of certain computer parts, e.g. CPUs and GPUs, along with internal logic that shuts down the computer if reasonable bounds are exceeded. It is however unwise to rely on such preventative measures, as it is not universally implemented, and may not prevent repeated incidents from permanently damaging the integrated circuit.
The design of an integrated circuit may also incorporate features to shut down parts of the circuit when it is idling, or to scale back the clock speed under low workloads or high temperatures, with the goal of reducing both power use and heat generation.
System cooling
Fan from Papst for racks.
Air cooling
While any method used to move air around or to computer enclosures would count as air cooling, fans are by far the most commonly used implement for accomplishing that task. The term computer fan usually refers to fans attached to computer enclosures, but may also be intended to signify any other computer fan, such as a CPU fan, GPU fan, a chipset fan, PSU fan, HDD fan, or PCI slot fans. Common fan sizes include 40, 60, 80, 90, 120, and 140 mm.
In desktops
Airflow through a desktop ATX case.
Desktop computers typically use one or more fans for heat management. Almost all desktop power supplies have at least one fan to exhaust air from the case. Most manufacturers recommend bringing cool, fresh air in at the bottom front of the case, and exhausting warm air from the top rear.
If there is more air being forced into the system than being pumped out (due to an imbalance in the number of fans), this is referred to as a "positive" airflow, as the pressure inside the unit would be higher than outside. A balanced or neutral airflow is the most efficient[citation needed], although a slightly positive airflow results in less dust build up if dust filters are used.
With recent researches and studies, some companies [which?] are making noiseless computers.
In high density computing
Data centers typically contain many racks of flat 1U servers. Air is drawn in at the front of the rack and exhausted at the rear. Because data centers typically contain such large numbers of computers and other power-consuming devices, they risk overheating of the various components if no additional measures are taken. Thus, extensive HVAC systems are used. Often a raised floor is used so the area under the floor may be used as a large plenum for cooled air and power cabling.
In laptop computing
Laptops are typically made to rest on a solid surface. Unfortunately a flat surface is the least desirable angle to dissipate heat, lower temperatures are achieved by a chimney effect when a laptop is set at an angle from horizontal[citation needed]. It is important to note that laptops are neither designed for nor should they be used on surfaces or in spaces which impede the free flow of air (such as carpet or bed linens), as heat damage and/or thermal shutdown/slow-down may occur.
Laptop stands are accessories which, besides raising the laptops screen to another height, are also meant to reduce airflow restrictions.
Liquid submersion cooling
An uncommon practice is to submerse the computer's components in a thermally conductive liquid. Personal computers, such as the Apple PowerMac G5, that are cooled in this manner do not generally require any fans or pumps, and may be cooled exclusively by passive heat exchange between the computer's parts, the cooling fluid and the ambient air. Extreme density computers such as the Cray-2 may use additional radiators in order to facilitate heat exchange.
The liquid used must have sufficiently low electrical conductivity in order for it not to interfere with the normal operation of the computer's components. If the liquid is somewhat electrically conductive, it may be necessary to insulate certain parts of components susceptible to electromagnetic interference, such as the CPU.[1] For these reasons, it is preferred that the liquid be dielectric.
Liquids commonly used in this manner include various liquids invented and manufactured for this purpose by 3M, such as Fluorinert. Various oils, including but not limited to cooking, motor and silicone oils have all been successfully used for cooling personal computers.[2]
Evaporation can pose a problem, and the liquid may require either to be regularly refilled or sealed inside the computer's enclosure. Liquid may also slowly seep into and damage components, particularly capacitors, causing an initially functional computer to fail after hours or days immersed.
Waste heat reduction
Where full-power, full-featured modern computers are not required, some companies opt to use less powerful computers or computers with fewer features. For example: in an office setting, the IT department may choose a thin client or a diskless workstation thus cutting out the heat-laden components such as hard drives and optical disks. These devices are also often powered with direct current from an external power supply brick which still wastes heat, but not inside the computer itself.
The components used can greatly affect the power consumption and hence waste heat. A VIA EPIA motherboard with CPU typically generates approximately 25 watts of heat whereas a Pentium 4 motherboard typically generates around 140 watts. While the former has considerably less computing power, both types are adequate and responsive for tasks such as word processing and spreadsheets. Choosing a LCD monitor rather than a CRT can also reduce power consumption and excess room heat.
Conductive and radiative cooling
Some laptop components, such as hard drives and optical drives, are commonly cooled by having them make contact with the computer's frame, increasing the surface area which can radiate and otherwise exchange heat.
Spot cooling
In addition to system cooling, various individual components usually have their own cooling systems in place. Components which are individually cooled include, but are not limited to, the CPU, GPU, hard disk, and the Northbridge chip. Some cooling solutions employ one or more methods of cooling, and may also utilize logic and/or temperature sensors in order to vary the power used in active cooling components.
Passive heat sink cooling
Passive heatsink fitted on a Intel GMA graphics chip
This involves attaching a block of machined metal to the part that needs cooling. An adhesive may be used, or more commonly for a personal computer CPU, a clamp is used to affix the heat sink right over the chip, with a thermally conductive pad or gel spread in-between. This block usually has fins and ridges to increase its surface area. The heat conductivity of metal is much better than that of air, and its ability to radiate heat is better than that of the component part it is protecting (usually an integrated circuit or CPU). Until recently, fan cooled aluminium heat sinks were the norm for desktop computers. Today many heat sinks feature copper base-plates or are entirely made of copper, and mount fans of considerable size and power.
Heat sinks tend to get less effective with time due to the build up of dust between their metal fins, which reduces the efficiency with which the heat sink transfers heat to the ambient air. Dust build up is commonly countered with canned air, which are used to blow away the dust along with any other unwanted excess material.
Passive heat sinks are commonly found on older CPUs, parts that do not get very hot (such as the chipset), and low-power computers.
Active heat sink cooling
This uses the same principle as a passive heat sink cooler, with the only difference being that a fan is directed to blow over or through the heat sink. This results in more air being blown through the heat sink, increasing the rate at which the heat sink can exchange heat with the ambient air. Active heat sinks are the primary method of cooling a modern day processor or graphics card.
The buildup of dust is greatly increased with active heat sink cooling as the fan is continually taking in the dust present in the surrounding air. As a result, dust removal procedures need to be exercised much more frequently than with passive heat sink methods.
Peltier cooling or thermoelectric cooling
In 1821 T. J. Seebeck discovered that different metals, connected at two different junctions, will develop a micro-voltage if the two junctions are held at different temperatures. This effect is known as the "Seebeck effect"; it is the basic theory behind the TEC (thermoelectric cooling).
In 1834 Jean Peltier discovered the inverse of the Seebeck effect, now known as the "Peltier effect". He found that applying a voltage to a thermocouple creates a temperature differential between two sides. This results in an effective, albeit extremely inefficient heat pump.
Modern TECs use several stacked units each composed of dozens or hundreds of thermocouples laid out next to each other, which allows for a substantial amount of heat transfer. A combination of bismuth and telluride is most commonly used for thermocouples.
Since TECs are active heat pumps, they are capable of cooling PC components below ambient temperatures, which is impossible with common radiator cooled water cooling systems and heatpipe HSFs.
Water cooling
DIY Watercooling setup showing 12v pump, CPU Waterblock and the typical application of a T-Line.
While originally limited to mainframe computers, computer watercooling has become a practice largely associated with overclocking in the form of either manufactured "kits" or in the form of DIY setups assembled from individually gathered parts. Lately watercooling has seen increasing use in pre-assembled desktop computers. Water cooling can extract more heat from the cooled parts, which makes it suitable for overclocking, and opposed to air cooling it is less influenced by the ambient temperature. One of its disadvantages is the potential for a coolant leak, which can damage electronic components. An advantage is that a water cooling system is not limited to one component, so it can cool the CPU, GPU and other components at the same time.
Heat pipe
A heat pipe is a hollow tube containing a heat transfer liquid. As the liquid evaporates, it carries heat to the cool end, where it condenses and then returns to the hot end (under capillary action). Heat pipes thus have a much higher effective thermal conductivity than solid materials. For use in computers, the heat sink on the CPU is attached to a larger radiator heat sink. Both heat sinks are hollow as is the attachment between them, creating one large heat pipe that transfers heat from the CPU to the radiator, which is then cooled using some conventional method. This method is expensive and usually used when space is tight (as in small form-factor PCs), or absolute quiet is needed (such as in computers used in audio production studios during live recording).
Phase-change cooling
An extremely effective way to cool the processor. A vapor compression phase-change cooler is a unit which usually sits underneath the PC, with a tube leading to the processor. Inside the unit is a compressor, the same type that cools a freezer. The compressor compresses a gas (or mixture of gases) which condenses it into a liquid. Then, the liquid is pumped up to the processor, where it passes through an expansion device, this can be from a simple capillary tube to a more elaborate thermal expansion valve. The liquid evaporates changing phase, thereby absorbing the heat from the processor, as it draws extra energy from its environment to accommodate this change (see latent heat). This evaporation can produce temperatures reaching around −15 to -150 degrees Celsius. The gas flows down to the compressor and the cycle begins over again. This way, the processor can be cooled to temperatures ranging from −15 to −150 degrees Celsius, depending on the load, wattage of the processor, the refrigeration system (see refrigeration) and the gas mixture used. This type of system suffers from a number of issues but mainly one must be concerned with dewpoint and proper insulation of all sub-ambient surfaces must be done otherwise the pipes will sweat dripping water on sensitive electronics.
Alternately a new breed of cooling system is being developed inserting a pump into the thermo siphon loop. This adds another degree of flexibility for the design engineer as the heat can now be effectively transported away from the heat source and either reclaimed or dissipated to ambient. Junction temperature can be tuned by adjusting the system pressure; higher pressure equals higher fluid saturation temperatures. This allows for smaller condensers, smaller fans and/or the effective dissipation of heat in a high ambient environment. These systems are in essence the next generation liquid cooling paradigm as they are approximately 10x more efficient than single phase water. Since the system uses a dielectric as the heat transport media leaks do not cause a catastrophic failure of the electric system.
This type of cooling is seen as a more extreme way to cool components, since the units are relatively expensive compared to the average desktop. They also generate a significant amount of noise, since they are essentially miniature refrigerators, however the compressor choice and air cooling system is the main determinant of this, allowing for flexibility for noise reduction based on the parts chosen.
Liquid nitrogen
Liquid nitrogen may be used to cool an overclocked PC.
As liquid nitrogen evaporates at -196 °C, far below the freezing point of water, it is valuable as a phase-change coolant, bringing the additional advantages of being non-toxic and non-combustible.
In a typical installation of liquid nitrogen cooling, fans blow air onto the heat sink of the CPU, as water is pumped through a pipe which ends over the heat sink, and similarly liquid nitrogen can be pushed out of a dewar through a pipe which ends over the heat sink. The short, yet wide nitrogen exhaust ends in a basing on the floor of the housing. Evaporating nitrogen pushes away water, which would otherwise condense and lead to short circuits or form ice. Overly drastic cooling will freeze out the dopant states and the semiconductors will stop working.
By welding an open pipe onto a heat sink, and insulating the pipe, it is possible to cool the processor either with liquid nitrogen, which has a temperature below −196°C, or dry ice. However, after the nitrogen evaporates, it has to be refilled. In the realm of personal computers, this method of cooling is seldom used in other contexts than overclocking trial-runs and record-setting attempts, as the CPU will usually expire within a relatively short period of time due to temperature stress caused by changes in internal temperature.
Soft cooling
Softcooling is the practice of utilizing software to take advantage of CPU power saving technologies to minimize energy use. This is done using halt instructions to turn off or put in standby state CPU subparts that aren't being used or by underclocking the CPU.
Undervolting
Undervolting is the practice of running the CPU or any other component with voltages below the device specifications. An undervolted component draws less power and thus produces less heat. However, this generally will make a processor unstable as it no longer has the voltage necessary to carry out instructions error free. As such, in most cases undervolting is accompanied by an underclocking of the processor itself. Keeping the speed/voltage ratio allows a system to be undervolted while maintaining stability. This technique is generally employed by those seeking low-noise systems, as less cooling is needed because of the reduction of heat production.
Cooling and overclocking
Extra cooling is usually required by those who run parts of their computer (such as the CPU and GPU) at higher voltages and frequencies than manufacturer specifications call for, called overclocking. Increasing performance by this modification of settings results in a greater amount of heat generated and thus increasing the risk of damage to components and/or premature failure.
The installation of higher performance, non-stock cooling may also be considered modding. Many overclockers simply buy more efficient, and often, more expensive fan and heat sink combinations, while others resort to more exotic ways of computer cooling, such as liquid cooling, Peltier effect heatpumps, heat pipe or phase change cooling.
There are also some related practices that have a positive impact in reducing system temperatures:
Heat sink lapping
Heat sink lapping is the smoothing and polishing of the contact (bottom) part of a heat sink to increase its heat transfer efficiency. The desired result is a contact area which has a more even surface, as a less even contact surface creates a larger amount of insulating air between the heat sink and the computer part it is attached to. Polishing the surface using a combination of fine sandpaper and abrasive polishing liquids can produce a mirror-like shine, an indicator of a very smooth metal surface. However, it should be noted that even a curved surface can become extremely reflective, yet not particularly flat, as is the case with curved mirrors; thus heat sink quality is based on overall flatness, more than optical properties. Lapping a high quality heat sink can damage it, because, although the heat sink may become shiny, it is likely that more material will be removed from the edges, making the heat sink less effective overall.
If attempted a piece of flat glass should be used as it self-levels as it cools and offers the most economical solution to producing a perfectly flat surface.
Use of exotic thermal conductive compounds
Some overclockers use special thermal compounds whose manufacturers claim to have a much higher efficiency than stock thermal pads. Heat sinks clean of any grease or other thermal transfer compounds have a very thin layer of these products applied, and then are placed normally over the CPU. Many of these compounds have a high proportion of silver as their main ingredient due to its high thermal conductivity. The resulting difference in the temperature of the CPU is measurable (several degrees celsius), but the heat transfer does appear to be much superior to stock compounds. Some people experience negligible gains and have called to question the advantages of these exotic compounds, calling the style of application more important than the compound itself. Also note that there may be a 'setting' or 'curing' period and negligible gains may improve over time as the compound reaches its optimum thermal conductivity.
Use of rounded cables
Most older PCs use flat ribbon cables to connect storage drives (IDE or SCSI). These large flat cables greatly impede airflow by causing drag and turbulence. Overclockers and modders often replace these with rounded cables, with the conductive wires bunched together tightly to reduce surface area. Theoretically, the parallel strands of conductors in a ribbon cable serve to reduce crosstalk (signal carrying conductors inducing signals in nearby conductors), but there is no empirical evidence of rounding cables reducing performance. This may be because the length of the cable is short enough so that the effect of crosstalk is negligible. Problems usually arise when the cable is not electromagnetically protected and the length is considerable, a more frequent occurrence with older network cables.
These computer cables can then be cable tied to the chassis or other cables to further increase airflow.
This is less of a problem with new computers that use Serial ATA which has a much thinner cable.
Airflow optimization
The colder the cooling medium (the air), the more effective the cooling. Cooling air temperature can be reduced by these guidelines:
Supply cool air to the hot components as directly as possible. Examples are air snorkels and tunnels that feed outside air directly and exclusively to the CPU or GPU cooler. For example, the BTX case design prescribes a CPU air tunnel.
Expel warm air as directly as possible. Examples are: Conventional PC (ATX) power supplies blow the warm air out the back of the case. Many dual-slot graphics card designs blow the warm air through the cover of the adjacent slot. There are also some aftermarket coolers that do this. Some CPU cooling designs blow the warm air directly towards the back of the case, where it can be ejected by a case fan.
Air that has already been used to spot-cool a component should not be reused to spot-cool a different component (this follows from the previous items). The ATX case design can be said to violate this rule, since the power supply gets its "cool" air from the inside of the case, where it has been warmed up already. The BTX case design also violates this rule, since it uses the CPU cooler's exhaust to cool the chipset and often the graphics card.
Prefer cool intake air, avoid inhaling exhaust air (outside air above or near the exhausts). For example, a CPU cooling air duct at the back of a tower case would inhale warm air from a graphics card exhaust. Moving all exhausts to one side of the case, conventionally the back, helps to keep the intake air cool.
Fewer fans strategically placed will improve the airflow internally within the PC and thus lower the overall internal case temperature in relation to ambient conditions. The use of larger fans also improves efficiency and lowers the amount of waste heat along with the amount of noise generated by the fans while in operation.
There is little agreement on the effectiveness of different fan placement configurations, and little in the way of systematic testing has been done. For a rectangular PC (ATX) case, a fan in the front with a fan in the rear and one in the top has been found to be a suitable configuration. However, AMD's (somewhat outdated) system cooling guidelines notes that "A front cooling fan does not seem to be essential. In fact, in some extreme situations, testing showed these fans to be recirculating hot air rather than introducing cool air."[3] It may be that fans in the side panels could have a similar detrimental effect -- possibly through disrupting the normal air flow through the case. However, this is unconfirmed and probably varies with the configuration.
NOTE:
Computer fan
A computer fan can be any fan inside a computer case used for cooling purposes, and may refer to fans that draw cooler air into the case from the outside, expel warm air from inside, or move air across a heatsink to cool a particular component. The use of fans and/or other hardware to cool a computer is sometimes referred to as active cooling.
Manufacturers of fans include, among others, Akasa, Arctic Cooling, Cooler Master, Delta, Nexus, Noctua, NorthQ, ebm-papst, Scythe, and Zalman.
Usage
As processors, graphics cards, RAM and other components in computers have increased in clock speed and power consumption, the amount of heat produced by these components as a side-effect of normal operation has also increased. These components need to be kept within a reasonable range to prevent overheating, instability, malfunction and damage leading to a shortened component lifespan.
While in earlier personal computers it was possible to cool most components using natural (or free) convection (passive cooling), more effective cooling has become a necessity on many components. To cool these components, fans are used to move dead air away from the components and draw cooler air over them. Fans attached to components are usually used in combination with a heatsink to increase the area of heated surface in contact with the air, thereby improving the efficiency of cooling.
In the IBM compatible PC market, the computer's PSU (power supply unit) has always used an exhaust fan to expel warm air from the PSU. Active cooling on CPUs started to appear on the Intel 80486, and by 1997 was standard on all desktop processors[1]. Chassis or case fans, usually one exhaust fan to expel heated air from the rear and optionally an intake fan to draw cooler air in through the front, became common with the arrival of the Pentium 4 in late 2000[1]. A third vent fan in the side of the PC, often located over the CPU, is also common. The GPU (graphics processing unit) on many modern graphics cards requires a heatsink and fan. In some cases, the northbridge chip on the motherboard requires a fan and heatsink. Other components such as the hard drives and RAM (More commonly RAM is cooled with attached RAM Heatsinks) may also be actively cooled, though as of 2007 this remains relatively unusual. It is not uncommon to find five or more fans in a modern PC. The most common RAM cooling application are RAM Heatsinks, which attach to the RAM itself. [1]
Cooling fan applications
Case mount
Used to aerate the case of the computer. The components inside the case which use active cooling cannot remove heat efficiently if the surrounding air is too hot. Case fans move air through the case, usually drawing cooler outside air in through the front (where it may also be drawn over the internal hard drive racks) and expelling it through the rear. There may be a third fan in the side or top of the case to draw outside air into the vicinity of the CPU, which is usually the largest single generator of heat. Case fans are usually 80 mm, 92 mm or 120 mm along each side. Because case fans are often the most readily visible form of cooling on a PC, decorative fans are widely available and may be lit with LEDs or made of UV-reactive plastic. Decorative grilles are also common. Decorative fans and accessories are popular with case modders. Air filters are often used over intake fans, to prevent dust from entering the case.
A power supply (PSU) fan often plays a double role, not only keeping the PSU itself from overheating, but also removing warm air from inside the case. Many modern PSUs expel the air from the rear, but only from the PSU itself. PSs with two fans are also available, which have a large fan on the bottom for removing case air and a smaller one on the back for expelling the warm air at a faster rate.
CPU fan
Used to cool the CPU (central processing unit).
See computer spot cooling.
Graphics card fan
Used to cool the GPU and/or memory on graphics cards. These fans were not necessary on older cards because of their low heat dissipation, but most modern graphics cards, especially those designed for 3D graphics and gaming, need their own dedicated cooling fans. Some of the higher powered cards can produce more heat than the CPU (over 190 watts[2]), so efficient cooling is especially important. Passive coolers for new video cards, however, are not unheard of, such as the Thermalright HR-03.
Chipset fan
Used to cool the northbridge of a motherboard's chipset or for system bus overclocking.
Other types of fans
Other less commonly encountered fans may include:
PCI slot fan: A fan mounted in one of the PCI slots, usually to supply additional cooling to the PCI and/or graphics cards.
Hard disk fan: A fan mounted next to or on a hard disk drive. This may be desirable on faster-spinning (e.g. 10,000 RPM) hard disks where heat production is higher.
CD Burner fan: Some internal CD and/or DVD burners included cooling fans.
Physical characteristics
The width and height of these usually square fans are measured in millimeters; common sizes include 60 mm, 80 mm, 92 mm and 120 mm. Fans with a round frame are also available; these are usually designed so that one may use a larger fan than the mounting holes would otherwise allow (i.e., a 120 mm fan with 90 mm holes). The amount of airflow which fans generate is typically measured in cubic-feet per minute (CFM), and the speed of rotation is measured in revolutions per minute (RPM). Often, computer enthusiasts choose fans which have a higher CFM rating, but produce less noise (measured in decibels, or dB), and some fans come with an adjustable RPM rating to produce less noise if the computer does not need much airflow. Fan speeds may be controlled manually (a simple potentiometer control, for example), thermally, or by the computer hardware or by software. It is also possible to run many 12V fans from the 5 V supply, at an expense of airflow, but with much reduced noise levels.
The type of bearing used in a fan can affect its performance and noise output. Most computer fans use one of the following bearing types:
Sleeve bearing fans use two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings may be more likely to fail at higher temperatures, and may perform poorly when mounted in any orientation other than vertical. The lifespan of a sleeve bearing fan may be around 40,000 hours at 50 °C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings, and are quieter at lower speeds early in their life, but can grow considerably noisier as they age.[3][4]
Rifle bearing fans are similar to sleeve bearing, but are even quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft.[5] The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
Ball bearing fans use a sealed bearing containing steel balls against which the axle rotates. Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable especially at higher temperatures, and quieter than sleeve bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be around 63,000 hours at 50 °C.[3][4]
Fluid bearing fans have the advantages of near-silent operation and high life expectancy (comparable to ball bearing fans). However, these fans tend to be the most expensive. The enter bearing fan is a variation of the fluid bearing fan, developed by Everflow[6].
Magnetic bearing or maglev fans, in which the fan is repelled from the bearing by magnetism.
Fan Connector
The standard connectors for computer fans are
3-pin Molex connector
This connector is used when connecting a fan to the motherboard or other circuit board. It is a small thick rectangular in-line female connector with two tabs on the outter-most edge of one long side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector.
4-pin Molex connector
this connector is used when connecting the fan directly to the power supply. It consists of to wires (red/12V and black/ground) leading to and splicing into a large in-line 4-pin male-to-female Molex connector.
Dell, Inc. proprietary
this connector is an expansion of a simple 3-pin female IC connector by adding two tabs to the middle of the connector on one side and a lock-tab on the other side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector and 3-pin Molex connector.
NOTE:
Manufacturers of fans include, among others, Akasa, Arctic Cooling, Cooler Master, Delta, Nexus, Noctua, NorthQ, ebm-papst, Scythe, and Zalman.
Usage
As processors, graphics cards, RAM and other components in computers have increased in clock speed and power consumption, the amount of heat produced by these components as a side-effect of normal operation has also increased. These components need to be kept within a reasonable range to prevent overheating, instability, malfunction and damage leading to a shortened component lifespan.
While in earlier personal computers it was possible to cool most components using natural (or free) convection (passive cooling), more effective cooling has become a necessity on many components. To cool these components, fans are used to move dead air away from the components and draw cooler air over them. Fans attached to components are usually used in combination with a heatsink to increase the area of heated surface in contact with the air, thereby improving the efficiency of cooling.
In the IBM compatible PC market, the computer's PSU (power supply unit) has always used an exhaust fan to expel warm air from the PSU. Active cooling on CPUs started to appear on the Intel 80486, and by 1997 was standard on all desktop processors[1]. Chassis or case fans, usually one exhaust fan to expel heated air from the rear and optionally an intake fan to draw cooler air in through the front, became common with the arrival of the Pentium 4 in late 2000[1]. A third vent fan in the side of the PC, often located over the CPU, is also common. The GPU (graphics processing unit) on many modern graphics cards requires a heatsink and fan. In some cases, the northbridge chip on the motherboard requires a fan and heatsink. Other components such as the hard drives and RAM (More commonly RAM is cooled with attached RAM Heatsinks) may also be actively cooled, though as of 2007 this remains relatively unusual. It is not uncommon to find five or more fans in a modern PC. The most common RAM cooling application are RAM Heatsinks, which attach to the RAM itself. [1]
Cooling fan applications
Case mount
Used to aerate the case of the computer. The components inside the case which use active cooling cannot remove heat efficiently if the surrounding air is too hot. Case fans move air through the case, usually drawing cooler outside air in through the front (where it may also be drawn over the internal hard drive racks) and expelling it through the rear. There may be a third fan in the side or top of the case to draw outside air into the vicinity of the CPU, which is usually the largest single generator of heat. Case fans are usually 80 mm, 92 mm or 120 mm along each side. Because case fans are often the most readily visible form of cooling on a PC, decorative fans are widely available and may be lit with LEDs or made of UV-reactive plastic. Decorative grilles are also common. Decorative fans and accessories are popular with case modders. Air filters are often used over intake fans, to prevent dust from entering the case.
A power supply (PSU) fan often plays a double role, not only keeping the PSU itself from overheating, but also removing warm air from inside the case. Many modern PSUs expel the air from the rear, but only from the PSU itself. PSs with two fans are also available, which have a large fan on the bottom for removing case air and a smaller one on the back for expelling the warm air at a faster rate.
CPU fan
Used to cool the CPU (central processing unit).
See computer spot cooling.
Graphics card fan
Used to cool the GPU and/or memory on graphics cards. These fans were not necessary on older cards because of their low heat dissipation, but most modern graphics cards, especially those designed for 3D graphics and gaming, need their own dedicated cooling fans. Some of the higher powered cards can produce more heat than the CPU (over 190 watts[2]), so efficient cooling is especially important. Passive coolers for new video cards, however, are not unheard of, such as the Thermalright HR-03.
Chipset fan
Used to cool the northbridge of a motherboard's chipset or for system bus overclocking.
Other types of fans
Other less commonly encountered fans may include:
PCI slot fan: A fan mounted in one of the PCI slots, usually to supply additional cooling to the PCI and/or graphics cards.
Hard disk fan: A fan mounted next to or on a hard disk drive. This may be desirable on faster-spinning (e.g. 10,000 RPM) hard disks where heat production is higher.
CD Burner fan: Some internal CD and/or DVD burners included cooling fans.
Physical characteristics
The width and height of these usually square fans are measured in millimeters; common sizes include 60 mm, 80 mm, 92 mm and 120 mm. Fans with a round frame are also available; these are usually designed so that one may use a larger fan than the mounting holes would otherwise allow (i.e., a 120 mm fan with 90 mm holes). The amount of airflow which fans generate is typically measured in cubic-feet per minute (CFM), and the speed of rotation is measured in revolutions per minute (RPM). Often, computer enthusiasts choose fans which have a higher CFM rating, but produce less noise (measured in decibels, or dB), and some fans come with an adjustable RPM rating to produce less noise if the computer does not need much airflow. Fan speeds may be controlled manually (a simple potentiometer control, for example), thermally, or by the computer hardware or by software. It is also possible to run many 12V fans from the 5 V supply, at an expense of airflow, but with much reduced noise levels.
The type of bearing used in a fan can affect its performance and noise output. Most computer fans use one of the following bearing types:
Sleeve bearing fans use two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings may be more likely to fail at higher temperatures, and may perform poorly when mounted in any orientation other than vertical. The lifespan of a sleeve bearing fan may be around 40,000 hours at 50 °C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings, and are quieter at lower speeds early in their life, but can grow considerably noisier as they age.[3][4]
Rifle bearing fans are similar to sleeve bearing, but are even quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft.[5] The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
Ball bearing fans use a sealed bearing containing steel balls against which the axle rotates. Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable especially at higher temperatures, and quieter than sleeve bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be around 63,000 hours at 50 °C.[3][4]
Fluid bearing fans have the advantages of near-silent operation and high life expectancy (comparable to ball bearing fans). However, these fans tend to be the most expensive. The enter bearing fan is a variation of the fluid bearing fan, developed by Everflow[6].
Magnetic bearing or maglev fans, in which the fan is repelled from the bearing by magnetism.
Fan Connector
The standard connectors for computer fans are
3-pin Molex connector
This connector is used when connecting a fan to the motherboard or other circuit board. It is a small thick rectangular in-line female connector with two tabs on the outter-most edge of one long side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector.
4-pin Molex connector
this connector is used when connecting the fan directly to the power supply. It consists of to wires (red/12V and black/ground) leading to and splicing into a large in-line 4-pin male-to-female Molex connector.
Dell, Inc. proprietary
this connector is an expansion of a simple 3-pin female IC connector by adding two tabs to the middle of the connector on one side and a lock-tab on the other side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector and 3-pin Molex connector.
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2008年10月23日星期四
Windows Security Center
The Windows Security Center is a component included with Microsoft's Windows XP (beginning with Service Pack 2) and Windows Vista operating systems that provides users with the ability to view the status of computer security settings and services. Windows Security Center also continually monitors these security settings, and informs the user via a pop-up notification balloon if there is a problem.
Overview
The Windows Security Center consists of three major components: A control panel, a Windows Service, and an application programming interface that is provided by Windows Management Instrumentation.
The control panel divides the monitored security settings into categories, the headings of which are displayed with a background color of light blue (green in Vista), yellow, or red. A category with a blue or green background indicates that the settings in the category are "healthy". A yellow background typically indicates that some or all of the settings in that category are not being monitored. A red background indicates that there is a problem that can expose the user's computer to problems.
A notification balloon indicating that there is no firewall protection.
The current state of these settings is determined by the Windows Service. This service, named "Security Center",[1] is started automatically when the computer starts, and takes responsibility for continually monitoring the system for changes, and also informs the user via a pop-up notification balloon if there is a problem. The settings are made available to the system through a Windows Management Instrumentation provider.
The primary interface which third-party anti-virus, anti-malware and firewall software vendors use to register with Windows Security Center is through the WMI provider. In Windows Vista, some Windows API calls were added to let applications retrieve the aggregate health status of Windows Security Center, and to receive notifications when the health status changes. Microsoft has offered suggestions that these new calls could be used by any application that wants to confirm that the system is in a healthy state before engaging in certain actions. An example they give is that a computer game could ensure that a firewall is running before connecting to a multi-player online game.
Version history
Windows XP SP2
The Windows Security Center in Windows XP Service Pack 2.
During a 2003 marketing campaign aimed at raising awareness of security, Microsoft learned from discussions with customers that there was confusion as to whether users were taking appropriate steps to protect their systems, or if the steps they were taking were effective.[2] From this research, Microsoft made the decision to include a prominent and visible control panel with Windows XP Service Pack 2 that would provide a consolidated view of the most important security features. Service Pack 2 was released in August 2004; this initial version provides monitoring of Windows Update, Windows Firewall, and the availability of an anti-virus software package. Third-party providers of firewall and anti-virus software packages were encouraged to make use of the Windows Security Center application programming interface to ensure that their software would be recognised.
Windows Vista
Windows Vista adds anti-malware software detection, monitoring of User Account Control, and monitoring of several Internet Explorer security settings. Windows Defender, Microsoft's anti-malware product, is included with Windows Vista by default, which Windows Security Center will monitor; a third-party anti-malware product can replace this. Another feature of the Windows Vista version is that it includes the ability to display logos of third-party products that have been registered with the Security Center.
Unlike Windows XP, in the beta versions of Windows Vista the Windows Security Center could not be disabled or overridden. Security software maker Symantec spoke out against this, noting that it would cause a great deal of consumer confusion because any security problems would be reported by both Windows Security Center and Symantec's tools at the same time.[3] McAfee, another large security software vendor, lodged similar complaints,[4] and in the end Microsoft allowed Windows Security Center to be disabled in the release version of Vista.[5]
Criticism and controversy
The initial release of Windows Security Center in 2004, while being promoted by Microsoft as an important step forward for the visibility of security in Microsoft Windows, was criticized by a number of groups of people for various reasons. PC Magazine ran a series of articles in their Security Watch newsletter titled "Windows XP SP2 Security Center Spoofing Threat" which outlined a design vulnerability which could "potentially allow attackers to spoof the state of security on a user's system while accessing data, infecting the system, or turning the PC into a zombie for spam or other purposes."[6] While the problem was made out to be trivially easy to exploit, as of 2006 there have been no notable exploits that take advantage of Windows Security Center.
NOTE:
System administrator
A system administrator, systems administrator, or sysadmin, is a person employed to maintain and operate a computer system and/or network. System administrators may be members of an information technology department.
The duties of a system administrator are wide-ranging, and vary widely from one organization to another. Sysadmins are usually charged with installing, supporting, and maintaining servers or other computer systems, and planning for and responding to service outages and other problems. Other duties may include scripting or light programming, project management for systems-related projects, supervising or training computer operators, and being the consultant for computer problems beyond the knowledge of technical support staff. A System Administrator must demonstrate a blend of technical skills and responsibility.
Skills
The subject matter of systems administration includes computer systems and the ways people use them in an organization. This entails a knowledge of operating systems and applications, as well as hardware and software troubleshooting, but also knowledge of the purposes for which people in the organization use the computers.
However, perhaps the most important skill to a system administrator is problem solving -- frequently under various sorts of constraints and stress. The sysadmin is on call when a computer system goes down or malfunctions, and must be able to quickly and correctly diagnose what is wrong and how best to fix it.
System administrators are not software engineers or developers. It is not usually within their duties to design or write new applications software. However, sysadmins must understand the behavior of software in order to deploy it and to troubleshoot problems, and generally know several programming languages used for scripting or automation of routine tasks.
Particularly when dealing with Internet-facing or business-critical systems, a sysadmin must have a strong grasp of computer security. This includes not merely deploying software patches, but also preventing break-ins and other security problems with preventive measures. In some organizations, computer security administration is a separate role responsible for overall security and the upkeep of firewalls and intrusion detection systems, but all sysadmins are generally responsible for the security of the systems in their keep.
Related fields
Many organizations staff other jobs related to systems administration. In a larger company, these may all be separate positions within a computer support or Information Services (IS) department. In a smaller group they may be shared by a few sysadmins, or even a single person.
A database administrator (DBA) maintains a database system, and is responsible for the integrity of the data and the efficiency and performance of the system.
A network administrator maintains network infrastructure such as switches and routers, and diagnoses problems with these or with the behavior of network-attached computers.
A security administrator is a specialist in computer and network security, including the administration of security devices such as firewalls, as well as consulting on general security measures.
A web administrator maintains web server services (such as IIS or Apache) that allow for internal or external access to web sites. Tasks include managing multiple sites, administering security, and configuring necessary components and software. Responsibilities may also include software change management.
Technical support staff respond to individual users' difficulties with computer systems, provide instructions and sometimes training, and diagnose and solve common problems.
A computer operator performs routine maintenance and upkeep, such as changing backup tapes or replacing failed drives in a RAID array. Such tasks usually require physical presence in the room with the computer; and while less skilled than sysadmin tasks require a similar level of trust, since the operator has access to possibly sensitive data.
In some organizations, a person may begin as a member of technical support staff or a computer operator, then gain experience on the job to be promoted to a sysadmin position.
Training
Unlike many other professions, there is no single path to becoming a system administrator. Many system administrators have a degree in a related field: computer science, information technology, computer engineering, information system management, or even a trade school program. Other schools have offshoots of their Computer Science program specifically for systems administration.
Some schools have started offering undergraduate degrees in Systems Administration. The first, RIT[1] started in 1992. Others such as Rensselaer Polytechnic Institute, Marist College, and Drexel University have more recently offered degrees in Information Technology.
As of 2008, only four U.S. universities, Rochester Institute of Technology[2], New York City College of Technology,Tufts, and Michigan Tech have graduate programs in system administration.[citation needed] In Norway, there is a special English-taught MSc program organized by Oslo University College [3] in cooperation with Oslo University, named "Masters programme in Network and System Administration." University of Amsterdam (UvA) offers a similar program[1], in cooperation with Hogeschool van Amsterdam (HvA). However, many other schools offer related graduate degrees in fields such as network systems and computer security.
One of the primary difficulties with teaching system administration as a formal university discipline, is that the industry and technology changes much faster than the typical textbook and coursework certification process. By the time a new textbook has spent years working through approvals and committees, the specific technology for which it is written may have changed significantly or is now obsolete.
In addition, because of the practical nature of systems administration and the easy availability of open-source server software, many systems administrators enter the field self-taught.
Generally, a prospective administrator will be required to have some experience with the computer system he or she is expected to manage. In some cases, candidates are expected to possess industry certifications such as the Microsoft MCSA, MCSE, Red Hat RHCE, Novell CNA, CNE, Cisco CCNA or CompTIA's A+ or Network+, Sun Certified SCNA, among others.
Sometimes, almost exclusively in smaller sites, the role of system administrator may be given to a skilled user in addition to or in replacement of his or her duties. For instance, it is not unusual for a mathematics or computing teacher to serve as the system administrator of a secondary school.
NOTE:
The duties of a system administrator are wide-ranging, and vary widely from one organization to another. Sysadmins are usually charged with installing, supporting, and maintaining servers or other computer systems, and planning for and responding to service outages and other problems. Other duties may include scripting or light programming, project management for systems-related projects, supervising or training computer operators, and being the consultant for computer problems beyond the knowledge of technical support staff. A System Administrator must demonstrate a blend of technical skills and responsibility.
Skills
The subject matter of systems administration includes computer systems and the ways people use them in an organization. This entails a knowledge of operating systems and applications, as well as hardware and software troubleshooting, but also knowledge of the purposes for which people in the organization use the computers.
However, perhaps the most important skill to a system administrator is problem solving -- frequently under various sorts of constraints and stress. The sysadmin is on call when a computer system goes down or malfunctions, and must be able to quickly and correctly diagnose what is wrong and how best to fix it.
System administrators are not software engineers or developers. It is not usually within their duties to design or write new applications software. However, sysadmins must understand the behavior of software in order to deploy it and to troubleshoot problems, and generally know several programming languages used for scripting or automation of routine tasks.
Particularly when dealing with Internet-facing or business-critical systems, a sysadmin must have a strong grasp of computer security. This includes not merely deploying software patches, but also preventing break-ins and other security problems with preventive measures. In some organizations, computer security administration is a separate role responsible for overall security and the upkeep of firewalls and intrusion detection systems, but all sysadmins are generally responsible for the security of the systems in their keep.
Related fields
Many organizations staff other jobs related to systems administration. In a larger company, these may all be separate positions within a computer support or Information Services (IS) department. In a smaller group they may be shared by a few sysadmins, or even a single person.
A database administrator (DBA) maintains a database system, and is responsible for the integrity of the data and the efficiency and performance of the system.
A network administrator maintains network infrastructure such as switches and routers, and diagnoses problems with these or with the behavior of network-attached computers.
A security administrator is a specialist in computer and network security, including the administration of security devices such as firewalls, as well as consulting on general security measures.
A web administrator maintains web server services (such as IIS or Apache) that allow for internal or external access to web sites. Tasks include managing multiple sites, administering security, and configuring necessary components and software. Responsibilities may also include software change management.
Technical support staff respond to individual users' difficulties with computer systems, provide instructions and sometimes training, and diagnose and solve common problems.
A computer operator performs routine maintenance and upkeep, such as changing backup tapes or replacing failed drives in a RAID array. Such tasks usually require physical presence in the room with the computer; and while less skilled than sysadmin tasks require a similar level of trust, since the operator has access to possibly sensitive data.
In some organizations, a person may begin as a member of technical support staff or a computer operator, then gain experience on the job to be promoted to a sysadmin position.
Training
Unlike many other professions, there is no single path to becoming a system administrator. Many system administrators have a degree in a related field: computer science, information technology, computer engineering, information system management, or even a trade school program. Other schools have offshoots of their Computer Science program specifically for systems administration.
Some schools have started offering undergraduate degrees in Systems Administration. The first, RIT[1] started in 1992. Others such as Rensselaer Polytechnic Institute, Marist College, and Drexel University have more recently offered degrees in Information Technology.
As of 2008, only four U.S. universities, Rochester Institute of Technology[2], New York City College of Technology,Tufts, and Michigan Tech have graduate programs in system administration.[citation needed] In Norway, there is a special English-taught MSc program organized by Oslo University College [3] in cooperation with Oslo University, named "Masters programme in Network and System Administration." University of Amsterdam (UvA) offers a similar program[1], in cooperation with Hogeschool van Amsterdam (HvA). However, many other schools offer related graduate degrees in fields such as network systems and computer security.
One of the primary difficulties with teaching system administration as a formal university discipline, is that the industry and technology changes much faster than the typical textbook and coursework certification process. By the time a new textbook has spent years working through approvals and committees, the specific technology for which it is written may have changed significantly or is now obsolete.
In addition, because of the practical nature of systems administration and the easy availability of open-source server software, many systems administrators enter the field self-taught.
Generally, a prospective administrator will be required to have some experience with the computer system he or she is expected to manage. In some cases, candidates are expected to possess industry certifications such as the Microsoft MCSA, MCSE, Red Hat RHCE, Novell CNA, CNE, Cisco CCNA or CompTIA's A+ or Network+, Sun Certified SCNA, among others.
Sometimes, almost exclusively in smaller sites, the role of system administrator may be given to a skilled user in addition to or in replacement of his or her duties. For instance, it is not unusual for a mathematics or computing teacher to serve as the system administrator of a secondary school.
NOTE:
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