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Computer architecture or digital computer organization is the conceptual design and fundamental operational structure of a computer system. It's ablueprint and functional description of requirements and design implementations for the various parts of a computer (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk ,

focusing largely on the way by which the central processing unit (CPU) performs internally and accesses addresses in memory.

It may also be defined as the science and art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals    (Dell Studio XPS 1340 Battery)    .

Computer architecture comprises at least three main subcategories:

  • Instruction set architecture, or ISA, is the abstract image of a computing system that is seen by a machine language (or assembly language) programmer, including the instruction set, word size,memory address modes, processor registers, and address and data formats      (Dell Studio XPS 1640 Battery)       .
  • Microarchitecture, also known as Computer organization is a lower level, more concrete and detailed, description of the system that involves how the constituent parts of the system are interconnected and how they interoperate in order to implement the ISA     (Dell Vostro 1710 Battery)   .
  • The size of a computer's cache for instance, is an organizational issue that generally has nothing to do with the ISA.
  • System Design which includes all of the other hardware components within a computing system such as  (Sony VGP-BPS13 battery)     :
  1. System interconnects such as computer buses and switches
  2. Memory controllers and hierarchies
  3. CPU off-load mechanisms such as direct memory access (DMA)
  4. Issues like multiprocessing     (Sony VGP-BPS13/B battery)       .

Once both ISA and microarchitecture have been specified, the actual device needs to be designed into hardware. This design process is called the implementation. Implementation is usually not considered architectural definition, but rather hardware design engineering   (Sony VGP-BPS13/S battery)    .

Implementation can be further broken down into three (not fully distinct) pieces:

  • Logic Implementation — design of blocks defined in the microarchitecture at (primarily) the register-transfer and gate levels     (Sony VGP-BPS13A/B battery)         .
  • Circuit Implementation — transistor-level design of basic elements (gates, multiplexers, latches etc.) as well as of some larger blocks (ALUs, caches etc.) that may be implemented at this level, or even (partly) at the physical level, for performance reasons      (Sony VGP-BPS13B/B battery)    .
  • Physical Implementation — physical circuits are drawn out, the different circuit components are placed in a chip floorplan or on a board and the wires connecting them are routed.

For CPUs, the entire implementation process is often called CPU design     (Sony VGP-BPL9 battery)    .

More specific usages of the term include more general wider-scale hardware architectures, such as cluster computing and Non-Uniform Memory Access (NUMA) architectures     (Sony VGP-BPS13B/B battery) .

History

The term “architecture” in computer literature can be traced to the work of Lyle R. Johnson, Muhammad Usman Khan and Frederick P. Brooks, Jr., members in 1959 of the Machine Organization department in IBM’s main research center     (Sony VGP-BPL11 battery) .

Johnson had the opportunity to write a proprietary research communication about Stretch, an IBM-developed supercomputer for Los Alamos Scientific Laboratory. In attempting to characterize his chosen level of detail for discussing the luxuriously embellished computer        (Sony VGP-BPL15 battery)    ,

he noted that his description of formats, instruction types, hardware parameters, and speed enhancements was at the level of “system architecture” – a term that seemed more useful than “machine organization”. Subsequently, Brooks, one of the Stretch designers    (Dell Inspiron E1505 battery)     ,

started Chapter 2 of a book (Planning a Computer System: Project Stretch, ed. W. Buchholz, 1962) by writing, “Computer architecture, like other architecture, is the art of determining the needs of the user of a structure and then designing to meet those needs as effectively as possible within economic and technological constraints”      (Dell Latitude E6400 battery)     .

Brooks went on to play a major role in the development of the IBM System/360 line of computers, where “architecture” gained currency as a noun with the definition “what the user needs to know”. Later the computer world would employ the term in many less-explicit ways       (HP Pavilion dv6000 Battery)     .

he way by which the CPU performs internally and accesses addresses in memory,” mentioned above, slip into the definition of computer architecture.

Computer architectures

There are many types of computer architectures    (Sony Vaio VGN-FZ31S battery)    :

  • Quantum computer vs Chemical computer
  • Scalar processor vs Vector processor
  • Non-Uniform Memory Access (NUMA) computers
  • Register machine vs Stack machine
  • Harvard architecture vs von Neumann architecture
  • Cellular architecture      (Sony VGN-FZ31S battery)

The quantum computer architecture holds the most promise to revolutionize computing.

Computer architecture topics      (Hp pavilion dv6000 battery)

Sub-definitions

Some practitioners of computer architecture at companies such as Intel and AMD use more fine distinctions:

  • Macroarchitecture — architectural layers that are more abstract than microarchitecture, e.g. ISA
  • Instruction Set Architecture (ISA) — as defined above   (SONY VGN-FZ38M Battery)
  • Assembly ISA — a smart assembler may convert an abstract assembly language common to a group of machines into slightly different machine language for different implementations      (SONY VGN-FZ31z Battery)
  • Programmer Visible Macroarchitecture — higher level language tools such as compilers may define a consistent interface or contract to programmers using them, abstracting differences between underlying ISA, UISA, and microarchitectures. E.g (Sony VGN-FZ31Z Battery)    .
  • the C, C++, or Java standards define different Programmer Visible Macroarchitecture — although in practice the C microarchitecture for a particular computer includes       (SONY VGN-FZ31E Battery)
  • UISA (Microcode Instruction Set Architecture) — a family of machines with different hardware level microarchitectures may share a common microcode architecture, and hence a UISA    (SONY  VGN-FZ31J Battery)   .
  • Pin Architecture — the set of functions that a microprocessor is expected to provide, from the point of view of a hardware platform. E.g. the x86 A20M, FERR/IGNNE or FLUSH pins, and the messages that the processor is expected to emit after completing a cache invalidation so that external caches can be invalidated     (SONY VGN-FZ31M Battery) .
  • Pin architecture functions are more flexible than ISA functions - external hardware can adapt to changing encodings, or changing from a pin to a message - but the functions are expected to be provided in successive implementations even if the manner of encoding them changes     (SONY VGN-FZ31B Battery)   .

The Role Of Computer Architecture

Computer Architecture: The Definition

The coordination of abstract levels of a processor under changing forces, involving design, measurement and evaluation. It also includes the overall fundamental working principle of the internal logical structure of a computer system  (SONY VGP-BPS13 Battery) .

It can also be defined as the design of the task-performing part of computers, i.e. how various gates and transistors are interconnected and are caused to function per the instructions given by an assembly language programmer   (Dell Inspiron 1320 Battery)   .

Instruction Set Architecture

  1. The ISA is the interface between the software and hardware.
  2. It is the set of instructions that bridges the gap between high level languages and the hardware    (Dell Inspiron 1320n Battery) .
  3. For a processor to understand a command, it should be in binary and not in High Level Language. The ISA encodes these values.
  4. The ISA also defines the items in the computer that are available to a programmer. For example, it defines data types, registers, addressing modes, memory organization etc     (Dell Inspiron 1464 Battery)  .
  5. Register are high speed storage for numbers that can be accessed by a processor. Data as well as instructions can be in a register.

Addressing modes are the ways in which the instructions locate their operands    (Dell Inspiron 1564 Battery)  .

Memory organization defines how instructions interact with the memory.

Computer Organization

Computer organization helps optimize performance-based products. For example, software engineers need to know the processing ability of processors  (Dell Inspiron 1764 Battery)    .

They may need to optimize software in order to gain the most performance at the least expense. This can require quite detailed analysis of the computer organization     (Dell Studio 1450 Battery)      .

For example, in a multimedia decoder, the designers might need to arrange for most data to be processed in the fastest data path and the various components are assumed to be in place and task is to investigate the organisational structure to verify the computer parts operates       (Dell Studio 1457 Battery)     .

Computer organization also helps plan the selection of a processor for a particular project. Multimedia projects may need very rapid data access, while supervisory software may need fast interrupts.

Sometimes certain tasks need additional components as well  (Dell Latitude D610 Battery)   .

For example, a computer capable of virtualization needs virtual memory hardware so that the memory of different simulated computers can be kept separated.

The computer organization and features also affect the power consumption and the cost of the processor   (Toshiba NB100 Battery) .

Design goals

Performance

Computer performance is often described in terms of clock speed (usually in MHz or GHz). This refers to the cycles per second of the main clock of the CPU       (Toshiba Satellite M65 battery)      .

However, this metric is somewhat misleading, as a machine with a higher clock rate may not necessarily have higher performance. As a result manufacturers have moved away from clock speed as a measure of performance.

Computer performance can also be measured with the amount of cache a processor has      (Toshiba Satellite M60 battery)   .

If the speed, MHz or GHz, were to be a car then the cache is like the gas tank. No matter how fast the car goes, it will still need to get gas. The higher the speed, and the greater the cache, the faster a processor runs.

Modern CPUs can execute multiple instructions per clock cycle, which dramatically speeds up a program       (Dell Latitude D830 Battery)     .

Other factors influence speed, such as the mix of functional units, bus speeds, available memory, and the type and order of instructions in the programs being run.

There are two main types of speed, latency and throughput. Latency is the time between the start of a process and its completion (Dell Latitude D620 Battery)   .

Throughput is the amount of work done per unit time. Interrupt latencyis the guaranteed maximum response time of the system to an electronic event (e.g. when the disk drive finishes moving some data). Performance is affected by a very wide range of design choices — for example, pipelining a processor usually makes latency worse (slower) but makes throughput better  (Dell Studio 1735 Battery)     .

Computers that control machinery usually need low interrupt latencies. These computers operate in a real-time environment and fail if an operation is not completed in a specified amount of time. For example, computer-controlled anti-lock brakes must begin braking almost immediately after they have been instructed to brake  (Dell Inspiron Mini 10 Battery)      .

The performance of a computer can be measured using other metrics, depending upon its application domain. A system may be CPU bound (as in numerical calculation), I/O bound (as in a webserving application) or memory bound (as in video editing). Power consumption has become important in servers and portable devices like laptops   (Sony VGN-FW11S Battery)   .

Benchmarking tries to take all these factors into account by measuring the time a computer takes to run through a series of test programs. Although benchmarking shows strengths, it may not help one to choose a computer. Often the measured machines split on different measures     (Sony VGN-FW11M Battery)   .

For example, one system might handle scientific applications quickly, while another might play popular video games more smoothly. Furthermore, designers have been known to add special features to their products, whether in hardware or software, which permit a specific benchmark to execute quickly but which do not offer similar advantages to other, more general tasks  (Sony VGN-FW139E/H battery) .

Power consumption

Power consumption is another design criterion that factors in the design of modern computers. Power efficiency can often be traded for performance or cost benefits     (Dell Latitude E5400 Battery)  .

With the increasing power density of modern circuits as the number of transistors per chip scales (Moore's law), power efficiency has increased in importance. Recent processor designs such as the Intel Core 2 put more emphasis on increasing power efficiency. Also, in the world of embedded computing, power efficiency has long been and remains the primary design goal next to performance (Dell Latitude E4200 Battery)  .

Computer cooling is required to remove the waste heat produced by computer components, to keep components within their safe operating temperature limits. Various cooling methods help to improve processor performance or reduce the noise of cooling fans     (Dell Vostro A840 Battery)     .

Components which produce heat and are susceptible to performance loss and damage include integrated circuits such as CPUs, chipset and graphics cards, along with hard drives (though excessive cooling of hard drives has been found to have negative effects). Overheated parts fail early and may give sporadic problems resulting in system freezes or crashes  (Dell Inspiron 300M Battery)    .

Both integral and peripheral means are used to keep the temperature of each component at a safe level. With regard to integral means, CPU and GPUsare designed with energy efficiency, including heat dissipation, in mind; though improved efficiency may only allow increased performance instead of reduced heat      (Dell Studio 1737 battery)    .

Peripheral means include 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    (Dell Inspiron E1505 battery) .

As a safety measure, many computers are designed to turn themselves off if the internal temperature exceeds a certain point. Alternatively, some have an option in their BIOS that allows the user to determine if the system emits an alarm beep or shuts itself down when the core temperature reaches the level set by the user     (Dell RM791 battery)   .

However, setting this incorrectly can result in hardware damage or erratic system behaviour.

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 (Dell XPS M1530 battery)    .

In operation, the temperature of a computer's components will rise until the heat lost to the surroundings is equal to the heat produced by the 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    (Dell XPS M2010 battery) .

Cooling can be hindered by:

  • 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 localized whirlpools of hot air in the case  (Dell Vostro 1000 battery) .
  • Poor heat transfer due to a lack of, or poor application of thermal compounds and sufficient surface area of heat sinks to radiate off the heat   (Acer Aspire One battery)      .

Damage prevention

Thermal sensors in some CPUs and GPUs can shut down the computer when high temperatures are detected. However, reliance on such measures may not prevent repeated incidents from permanently damaging the integrated circuit      (Toshiba Satellite P10 Battery)     .

An integrated circuit may also 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.

Air cooling

Fans are most commonly used for air cooling   (SONY VGN-FZ210CE Battery)    .

A computer fan may be attached to the computer case, or attached to a CPU, GPU, chipset, PSU, hard drive or PCI slot. Common fan sizes include 40, 60, 80, 92, 120, and 140 mm. Recently, 200mm fans have begun to creep into the performance market, as well as even larger sizes such as 230 and 240mm      (Dell Precision M70 Battery)   .

In desktops

Desktop computers typically use one or more fans for cooling. 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    (Toshiba Satellite L305 Battery) .

If there is more air being forced into the system than is being pumped out (due to an imbalance in the number or strength 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, although a slightly positive airflow results in less dust build up if dust filters are used    (Toshiba Satellite T4900 Battery)    .

Negative pressure inside the case can create problems such as clogged optical drives due to sucking in air (and dust).

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 (Toshiba PA3399U-2BRS battery)    .

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   (Toshiba Satellite A200 Battery)   .

Another way of accommodating large numbers of systems in a small space are blade chassis. In contrast to the horizontal orientation of flat servers, blade chassis are often oriented vertically. This vertical orientation facilitates convection. When the air is heated by the hot components, it tends to flow to the top on its own, creating a natural air flow along the boards    (Toshiba Satellite 1200 Battery) .

This stack effect can help to achieve the desired air flow and cooling. Some manufacturers expressly take advantage of this effect.

In laptop computing

Most laptops use air cooling in order to keep the CPU and other components within their operating temperature range  (Toshiba Satellite M300 Battery)     .

Because the fan's air is forced through a small port, the fan and heatsinks can be clogged by dust or be obstructed by objects placed near the port. This can cause overheating, and can be a cause of component failure in laptops. The severity of this problem varies with laptop design, its use and power dissipation     WD passport essential (500GB/640GB) .

With recent reductions in CPU power dissipation, this problem can be anticipated to reduce in severity.

Liquid submersion cooling

An uncommon practice is to submerge the computer's components in a thermally conductive liquid     WD passport essential (250GB/320GB) .

Personal computers 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 component density supercomputers such as the Cray-2 and Cray T90used additional liquid to chilled liquid heat exchangers in order to facilitate heat removal     WD  passport essential SE (750GB/1TB)    .

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   WD  passport elite(250GB/320GB) .

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       WD passport elite(500GB/640GB) .

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      WD  passport studio for Mac(320GB/500GB) .

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     WD  passport studio for Mac(500GB/640GB) .

For example: in an office setting, the ITdepartment 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       WD  Elements series(250GB/320GB) .

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 spreadsheetsWD  Elements SE(500GB/640GB) .

Choosing a LCD monitor rather than a CRT can also reduce power consumption and excess room heat, as well as the added benefit of increasing available physical desk space.

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    WD Elements SE(750GB/1TB) .

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, GPUand the Northbridge chip    WD  Elements desktop(500GB/640GB) .

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 heat-sink cooling involves attaching a block of machined or extruded metal to the part that needs cooling   WD  Elements desktop(750GB/1TB) .

A thermal adhesive may be used. More commonly for a personal-computer CPU, a clamp holds the heat sink directly over the chip, with a thermal grease or thermal pad spread 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 it radiates heat better than does the component that it is protecting (usually an integrated circuit or CPU)      WD  Elements desktop(1.5 TB/2TB) .

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.

Dust buildup between the metal fins of a heat sink gradually reduces efficiency, but can be countered with a gas duster by blowing away the dust along with any other unwanted excess material     WD  passport essential SE (750GB/1TB)--USB 3.0) .

Passive heat sinks are commonly found on older CPUs, parts that do not get very hot (such as the chipset), and low-power computers.

Usually a heat-sink is attached to the integrated heat spreader (IHS), essentially a large, flat plate attached to the CPU, with conduction paste layered between      WD  passport essential (500GB/640GB) .

This dissipates or spreads the heat locally. Unlike a heat sink, a spreader is meant to redistribute heat, not to remove it. In addition, the IHS protects the fragile CPU.

Passive cooling involves no fan noise     WD  passport for Mac(320GB/500GB) .

Active heat-sink cooling

Active heat-sink cooling uses the same principle as passive, with the addition of a fan that blows over or through the heat sink. The air movement increases the rate at which the heat sink can exchange heat with the ambient air     WD  passport for Mac(640GB/1TB) .

Active heat sinks are the primary method of cooling modern processors and graphics cards.

The buildup of dust is greatly increased with active heat-sink cooling, because the fan continually takes in the dust present in the surrounding air      My book essential 4 generation  (640GB/1TB) .

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)     WD  My book essential 4 generation( 1.5TB/2TB) .

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      WD  My book elite( 1TB/1.5TB) .

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 ofheat transfer. A combination of bismuth and telluride is most commonly used for thermocouples.

As active heat pumps, TECs can cool the surface of components below ambient temperatures      WD  My book studio(1TB/2TB) .

This is impossible with common radiator cooled water cooling systems and heatpipe HSFs.

Water cooling

While originally limited to mainframe computers, water cooling has become a practice largely associated with overclocking in the form of either manufactured kits, or in the form of do-it-yourself setups assembled from individually gathered parts  WD  My book essential 4 generation( 1.5TB/2TB) .

The past few years has seen water cooling increasing its popularity with pre-assembled, moderate to high performance, desktop computers. Water has the ability to dissipate more heat from the parts being cooled than the various types of metals used in heatsinks, making it suitable for overclocking and high performance computer applications       WD  My book elite(640GB/2TB) .

Advantages to water cooling include the fact that a system is not limited to cooling one component, but can be set up to cool the central processing unit, graphics processing unit, and/or other components at the same time with the same system. As opposed to air cooling, water cooling is also influenced less by the ambient temperature      Seagate  expansion portable (750GB/1TB) .

Water cooling's comparatively low noise-level compares favorably to that of active cooling, which can become quite noisy. One disadvantage to water cooling is the potential for a coolant leak. Leaked coolant can damage any electronic components it comes in contact with      Seagate  expansion portable (320GB/500GB) .

Another drawback to water cooling is the complexity of the system; an active heat sink is much simpler to build, install, and maintain than a water cooling solution.

Heat pipe

A heat pipe is a hollow tube containing a heat transfer liquid       Seagate  expansion (1.5TB/2TB) .

As the liquid evaporates, it carries heat to the cool end, where it condenses and then returns to the hot end (under capillary action, or, in earlier implementations, under gravitation). Heat pipes thus have a much higher effective thermal conductivity than solid materials       Seagate  Freeagent Desktop (500GB/1TB) .

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        Seagate  Freeagent Go(250GB/320GB) .

This method is expensive and usually used when space is tight (as in small form-factor PCs and laptops), or absolute quiet is needed (such as in computers used in audio production studios during live recording). Because of the efficiency of this method of cooling, many desktop CPUs and GPUs, as well as high end chipsets, use heat pipes in addition to active fan-based cooling to remain within safe operating temperatures      Seagate  Freeagent Go(500GB/640GB) .

A new design wrinkle is known as HDT for Heatpipe Direct Touch. In this usage, the heat pipe is in direct contact with the CPU chip skin. Heatpipe Direct Touch was first introduced in the Zaward ZikaRay ZIKA-01 heatsink on February 2007, using a patent obtained from Golden Sun News Techniques Corporation in Taiwan       Seagate  Freeagent Go(750GB/1TB) .

Phase-change cooling

Phase-change cooling is 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 of the same type as in a window air conditioner       Seagate  Freeagent Goflex(250GB/320GB) .

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      Seagate Freeagent Goflex(500GB/640GB) .

The liquid evaporates (changing phase), absorbing the heat from the processor as it draws extra energy from its environment to accommodate this change (see latent heat). The evaporation can produce temperatures reaching around ?15 to -150  degrees Celsius    Seagate  Freeagent Goflex(750GB/1TB) .

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   Seagate  Freeagent Goflex Pro(500GB/750GB) .

This type of system suffers from a number of issues but mainly one must be concerned with dew point and the proper insulation of all sub-ambient surfaces that must be done (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     Seagate  Freeagent Goflex desktop(1TB/2TB) .

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      Seagate  Freeagent go for Mac(320GB/640GB) .

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 10 times more efficient than single phase water    Samsung  G2 protable (250gb/320GB) .

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       Samsung  G2 protable (500GB/640GB) .

They also generate a significant amount of noise, since they are essentially 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   Samsung  S2 protable (320GB/500GB) .

Liquid nitrogen

In a typical installation of liquid nitrogen cooling, a copper or aluminum pipe is mounted on top of the processor or graphics card. After being heavily insulated against condensation, the liquid nitrogen is poured into the pipe, resulting in temperatures well below -100°C    Samsung S1 Mini (120GB/160GB).

Evaporation devices ranging from cut out heat sinks with pipes attached to custom milled copper containers are used to hold the nitrogen as well as to prevent large temperature changes. However, after the nitrogen evaporates, it has to be refilled. In the realm of personal computers  Samsung  S1 Mini (250GB/320GB) ,

this method of cooling is seldom used in contexts other than overclocking trial-runs and record-setting attempts, as the CPU will usually expire within a relatively short period of time due to temperaturestress caused by changes in internal temperature.

Although liquid nitrogen is non-flammable, it can condense oxygen directly from air  Samsung story station (1TB/1.5TB) .

Mixtures of liquid oxygen and flammable materials can be dangerously explosive.

Liquid helium

Liquid helium, colder than liquid nitrogen, has also been used for cooling. Liquid helium evaporates at -269 °C, and temperatures ranging from -230 to -240 °C have been measured from the heatsink    Samsung Story station (1.5TB/2TB) .

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

Samsung story station Esata(1TB/1.5TB) .

Undervolting

Undervolting is a 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    Samsung  G3 station (1TB/1.5TB) .

The ability to do this varies by manufacturer, product line, and even different production runs of the same exact product (as well as that of other components in the system), but modern processors are typically shipped with voltages higher than strictly necessary       Maxtor  one touch 4 plus (500GB/750GB) .

This provides a buffer zone so that the processor will have a higher chance of performing correctly under sub-optimal conditions, such as a lower quality mainboard (motherboard). However, too low a voltage will not allow the processor to function correctly, producing errors, system freezes or crashes, or the inability to turn the system on    Maxtor one touch 4 plus (1TB/1.5TB) .

(Undervolting too far does not typically lead to hardware damage, though in worst-case scenarios, program or system files can be corrupted)

This technique was generally employed by those seeking low-noise systems, as less cooling is needed because of the reduction of heat production        Maxtor black diamond (320GB/500GB) .

Since the popularity of hand-held or remote computers (Unmanned vehicles, mobile & cordless phones/camera/viewers, etc), undervolting is used to prolong battery endurance.

Integrated chip cooling techniques

Conventional cooling techniques all attach their “cooling” component to the outside of the computer chip, or via IHS and/or heat sinks      Maxtor cool black(640GB/1TB) .

This “attaching” technique will always exhibit some thermal resistance, reducing its effectiveness. The heat can be more efficiently and quickly removed by directly cooling the local hot spots. At these locations, power dissipation of over 300W/cm2 (typical CPU are less than 100W/cm2, although future systems are expected to exceed 1000W/cm2 ) can occur    Maxtor Black diamond (320GB/500GB) .

This form of local cooling is essential to developing high power density chips. This ideology has led to the investigation of integrating cooling elements into the computer chip. Currently there are two techniques: micro-channel heat sinks, and jet impingement cooling

Hitachi  simple touch (250GB/320GB) .

In micro-channel heat sinks, channels are fabricated into the silicon chip (CPU), and coolant is pumped through them. The channels are designed with very large surface area which results in large heat transfers. Heat dissipation of 3000W/cm2 has been reported with this technique  Hitachi simple touch (320GB/500GB) .

In comparison to the Sun power density of around 7400W/cm2. The heat dissipation can be further increased if two-phase flow cooling is applied. Unfortunately the system requires large pressure drops, due to the small channels, and the heat flux is lower with dielectric coolants used in electronic cooling    Hitachi  life studio (320GB/500GB) .

Another local chip cooling technique is jet impingement cooling. In this technique, a coolant is flown through a small orifice to form a jet. The jet is directed toward the surface of the CPU chip, and can effectively remove large heat fluxes. Heat dissipation of over 1000W/cm2has been reported        Hitachi life studio (250GB/320GB) .

The system can be operated at lower pressure in comparison to the micro-channel method. The heat transfer can be further increased using two-phase flow cooling and by intergrading return flow channels (hybrid between micro-channel heat sinks and jet impingement cooling)    Hitachi  life studio platinum (250GB/320GB) .

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    Hitachi life studio platinum (320GB/500GB) .

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    Hitachi life studio desk (500GB/1TB) .

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      Hitachi life studio plus (320GB/500GB) :

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    Hitachi life studio plus (320GB/500GB) .

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. Even a curved surface can become extremely reflective, yet not particularly flat, as is the case with curved mirrors    Hitachi X mobile (250GB/320GB) ;

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      Hitachi X mobile(320GB/500GB) .

If attempted, a piece of float 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    Hitachi  XL (1TB/2TB) .

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    Toshiba canvio portable(320GB/500GB) .

The resulting difference in the temperature of the CPU is measurable (several celsius degrees), so the heat transfer does appear to be 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    Toshiba  canvio portable(750GB/1TB) .

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  Toshiba  anvio for Mac(500GB/750GB) .

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  Toshiba  canvio for Mac(750GB/1TB) .

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    Toshiba External HDD –portable(320GB/500GB) .

This is less of a problem with new computers that use Serial ATA which has a much narrower cable

Toshiba portable(500GB/640GB) .

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