Computer cooling

( from wikipedia )











System cooling












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, 92 and 120 mm.

Liquid submersion cooling
An uncommon practice is to submerse the computer's components in a thermally conductive liquid. 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 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. 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.
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 a computer that initially functions to fail after hours or days immersed.There is an application on file with the United States Patent Office concerning liquid submersion cooling. Many cases of prior art appear to exist, making the issuance of this patent questionable. The application number for this patent is 20070268669.

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 method of cooling, and may also utilize logic and/or temperature sensors in order to vary the power used in active cooling components.

Cooling and overclocking
Extra cooling is usually required by those who run parts of their computer (such as the CPU and graphics card) at higher voltages or 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 smoothening 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, as 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 plate 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 specialty 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, and the heat transfer does appear to be much superior to stock compounds (several degrees celsius). However, 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 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 electro-magnetically 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 cooler 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." 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.

Video card

( from wikipedia )








Graphics processing unit (GPU)
A GPU is a dedicated graphics microprocessor optimized for floating point calculations which are fundamental to 3D graphics rendering. The main attributes of the GPU are the core clock rate, which typically ranges from 250 MHz to 1200 MHz in modern cards, and the number of pipelines (vertex and fragment shaders), which translate a 3D image characterized by vertices and lines into a 2D image formed by pixels.

Video memory
If the video card is integrated in the motherboard, it will use the computer RAM memory (lower throughput). If it is not integrated, the video card will have its own video memory which is called Video RAM or VRAM. The VRAM capacity of most modern video cards range from 128 to 1024 MB. Before 2003, the VRAM was typically based on DDR technology. During and after that year, manufacturers moved towards the vastly superior DDR2, GDDR3 and GDDR4. The memory clock rate in modern cards are generally between 400 MHz and 1.6 GHz. A very important element of the video memory is the Z-buffer, which manages the depth coordinates in 3D graphics.

Video BIOS
The video BIOS or firmware chip is a chip that contains the basic program that governs the video card's operations and provides the instructions that allow the computer and software to interface with the card. It contains information on the memory timing, operating speeds and voltages of the processor and ram and other information. It is possible to re-flash a BIOS (enable factory-locked settings for higher performance) although this is typically only done by video card overclockers, and has the potential to irreversibly damage the card.

RAMDAC
Random Access Memory Digital-to-Analog Converter. RAMDAC takes responsibility for turning the digital signals produced by the computer processor into an analog signal which can be understood by the computer display. Depending on the number of bits used and the RAMDAC data transfer rate, the converter will be able to support different computer display refresh rates. With CRT displays, it is best to work over 75 Hz and never under 60 Hz, in order to minimise flicker. (With LCD displays, flicker is not a problem.) Due to the growing popularity of digital computer displays and the migration of some of its functions to the motherboard, the RAMDAC is slowly disappearing. All current LCD and plasma displays and TVs work in the digital domain and do not require a RAMDAC. There are few remaining legacy LCD and plasma displays which feature analog inputs (VGA, component, SCART etc.) only; these do require a RAMDAC but they reconvert the analog signal back to digital before they can display it, with the unavoidable loss of quality stemming from this digital-to-analog-to-digital conversion.

Cooling devices











Heat sink with fan attached.
Due to video card work charge, high temperatures are reached, which can cause a breakdown. Cooling devices are incorporated to avoid excessive heat. There are two types of cooling devices, and both can be used at the same time:

• Heat sink: generally referred to as a passive cooling device, it has no moving parts and, therefore, is soundless and very reliable; it absorbs and dissipates heat from the GPU using thermal contact (by either direct or radiant contact with a cooling medium such as air). Its effectiveness depends on its size and other characteristics including shape and material (generally copper or aluminium).
• Computer fan: usually known as an active cooling device, it has moving parts to push hot air away from the video card and as such will generate a small amount of noise. It is more effective than a heat sink at cooling, but due to the moving parts is far less reliable than a passive heat-sink.
• Water Block (See: liquid cooling): uses liquid and heat sinks to cool the GPU. This method is used less often but is much more favorable to both other options as it is more effective than a fan and soundless just like a passive cooling device.
  
  

RAM

(From Wikipedia)










Types of RAM
Modern types of writable RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM), EPROM, EEPROM and Flash. Some types have circuitry to detect and/or correct random faults called memory errors in the stored data, using parity bits or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask to permanently enable/disable selected transistors, instead of storing a charge in them.
As both SRAM and DRAM are volatile, other forms of computer storage, such as disks and magnetic tapes, have been used as "permanent" storage in traditional computers. Newer products such as PDAs and small music players (up to 16 GB in Jan 2007) may not have hard disks however, but often rely on flash memory to maintain data between sessions of use; the same can be said about products such as mobile phones, advanced calculators, synthesizers etc; even certain categories of PC have begun replacing magnetic disk with so called flash drives. There are two basic types of flash memory: the NOR type, which is capable of true random access, and the NAND type, which is not; the former is therefore often used in place of ROM, while the latter is used in most memory cards and solid-state drives, due to a lower price.

DDR2 (from wikipedia )







A 512 MiB DDR2 533 module with BGA chips. DDR2 is a 240-pin module
Like all SDRAM implementations, DDR2 stores memory in memory cells that are activated with the use of a clock signal to synchronize their operation with an external data bus. Like DDR before it, DDR2 cells transfer data both on the rising and falling edge of the clock (a technique called "dual pumping"). The key difference between DDR and DDR2 is that in DDR2 the bus is clocked at twice the speed of the memory cells, so four words of data can be transferred per memory cell cycle. Thus, without speeding up the memory cells themselves, DDR2 can effectively operate at twice the bus speed of DDR.
DDR2's bus frequency is boosted by electrical interface improvements, on-die termination, prefetch buffers and off-chip drivers. However, latency is greatly increased as a trade-off. The DDR2 prefetch buffer is 4 bits deep, whereas it is 2 bits deep for DDR and 8 bits deep for DDR3. While DDR SDRAM has typical read latencies of between 2 and 3 bus cycles, DDR2 may have read latencies between 4 and 6 cycles. Thus, DDR2 memory must be operated at twice the bus speed to achieve the same latency.
Another cost of the increased speed is the requirement that the chips are packaged in a more expensive and more difficult to assemble BGA package as compared to the TSSOP package of the previous memory generations such as DDR and SDRAM. This packaging change was necessary to maintain signal integrity at higher speeds.
Power savings are achieved primarily due to an improved manufacturing process through die shrinkage, resulting in a drop in operating voltage (1.8 V compared to DDR's 2.5 V). The lower memory clock frequency may also enable power reductions in applications that do not require the highest available speed.

Relation to GDDR memory
The first commercial product to claim using the "DDR2" technology was the NVIDIA GeForce FX 5800 graphics card. However, it is important to note that this GDDR-2 memory used on graphics cards is not DDR2 per se, but rather an early midpoint between DDR and DDR2 technologies. Using "DDR2" to refer to GDDR-2 is a colloquial misnomer. In particular, the performance-enhancing doubling of the I/O clock rate is missing. It had severe overheating issues due to the nominal DDR voltages. ATI has since designed the GDDR technology further into GDDR3, which is more true to the DDR2 specifications, though with several additions suited for graphics cards.
GDDR3 is now commonly used in modern graphics cards and some tablet PCs. However, further confusion has been added to the mix with the appearance of budget and mid-range graphics cards which claim to use "DDR2". These cards actually use standard DDR2 chips designed for use as main system memory. These chips cannot achieve the clock speeds that GDDR3 can but are inexpensive enough to be used as memory on mid-range cards.

DDR3 ( from wikipedia)
DDR3 memory comes with a promise of a power consumption reduction of 30% compared to current commercial DDR2 modules due to DDR3's 1.5 V supply voltage, compared to DDR2's 1.8 V or DDR's 2.5 V. This supply voltage works well with the 90 nm fabrication technology used for most DDR3 chips. Some manufacturers further propose to use "dual-gate" transistors to reduce leakage of current.
The main benefit of DDR3 comes from the higher bandwidth made possible by DDR3's 8 bit deep prefetch buffer, whereas DDR2's is 4 bits, and DDR's is 2 bits deep.
Theoretically, these modules could transfer data at the effective clock rate of 800–1600 MHz (using both edges of a 400–800 MHz I/O clock), compared to DDR2's current range of effective 400–800 MHz (200–400 MHz clock) or DDR's range of 200–400 MHz (100–200 MHz). To date, such bandwidth requirements have been mainly found in the graphics market, where fast transfer of information between framebuffers is required.
Prototypes were announced in early 2005, and products are appearing on the market as of mid-[2007], in the form of motherboards based on Intel's P35 "Bearlake" chipset and memory DIMMs at speeds up to DDR3-1600. AMD's roadmap indicates their own adoption of DDR3 to come in 2008.
DDR3 DIMMs have 240 pins, the same number as DDR2, and are the same size, but are electrically incompatible and have a different key notch location.
GDDR3 memory, with a similar name but an entirely dissimilar technology, has been in use for several years in high-end graphic cards such as ones from NVIDIA or ATI Technologies, and as graphics system memory on the Sony Playstation 3. It has sometimes been incorrectly referred to as "DDR3".

Features
DDR3 SDRAM Components:
Introduction of asynchronous RESET pin
Support of system level flight time compensation
On-DIMM Mirror friendly DRAM pin out
Introduction of CWL (CAS Write Latency) per speed bin
On-die IO calibration engine
READ and WRITE calibration
DDR3 Modules:
Fly-by command/address/control bus with On-DIMM termination
High precision calibration resistors
Advantages compared to DDR2
Higher bandwidth performance increase (up to effective 1600 MHz)
Performance increase at low power (longer battery life in laptops)
Enhanced low power features
Improved thermal design (cooler)
Disadvantages compared to DDR2
Commonly higher CAS Latency
Generally costs much more than equivalent DDR2 memory.

PC case

Computer case (from wikipedia )













Sizes
Cases can come in many different sizes, or form factors. The size and shape of a computer case is usually determined by the form factor of motherboard that it is designed to accommodate, since this is the largest and most central component of most computers. Consequently, personal computer form factors typically specify only the internal dimensions and layout of the case. Form factors for rack-mounted and blade servers may include precise external dimensions as well, since these cases must themselves fit in specific enclosures.
For example, a case designed for an ATX motherboard and power supply may take on several external forms, such as a vertical tower (designed to sit on the floor) or a flat desktop or pizza box (designed to sit on the desk under the computer's monitor). Full-size tower cases are typically larger in volume than desktop cases, with more room for drive bays and expansion slots. Desktop cases—and mini-tower cases designed for the reduced microATX form factor—are popular in business environments where space is at a premium.










As of 2007, the most popular form factor for desktop computers is ATX, although microATX and small form factors have become very popular for a variety of uses. Companies like Shuttle Inc. and AOpen have popularized small cases, for which FlexATX is the most common motherboard size. Apple Computer has also produced the Mac Mini computer, which is similar in size to a standard Template:Convert/inch CD-ROM drive.
Layout
Computer cases usually include sheet metal enclosures for a power supply unit and drive bays, as well as a rear panel that can accommodate peripheral connectors protruding from the motherboard and expansion slots. Most cases also a power button or switch, a reset button, and LEDs to indicate power status, hard drive usage, and network activity. Some cases include built-in I/O ports (such as USB and headphone ports on the front of the case). Such a case will also include wires needed to connect these ports to the motherboard.