Primary Components of a Computer

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These are the components that will be the core of your new computer. It is impractical to put together a PC compatible computer without these components and a bare set of peripherals.

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Exploded view of a personal computer:
1 Monitor
2 Motherboard
3 CPU (Microprocessor)
4 ATA sockets
5 Main memory (RAM)
6 Expansion cards
7 Power supply unit
8 Optical disc drive
9 Hard disk drive (HDD)
10 Keyboard
11 Mouse

Chassis and Power Supply
In earlier eras most cases were beige, and since most components drew far less power than similar components do now, power supplies received little attention. Recently, however, cases for the home market have become considerably more elaborate, with lights, side windows, glow-in-the-dark cables and other shiny/glowing embellishments. Cases now come in a plethora of styles and colors to suit anyone’s taste. And as current components require much more power, power supply quality and size is an important issue.

If you are only building an office computer, the style of case will be of little concern to you. You might want an inexpensive ATX case (ATX is a specification which refers to the size of the motherboard. Any ATX motherboard, and the parts designed therefore, will fit in any ATX case), and an inexpensive power supply as you won’t be running a high-end processor or graphics card. As a guide, you’ll want a power supply with a rating of more than 300 watts; any less won’t reliably power modern components. Most case/PSU bundles are adequate, but tend to feature a lower quality power supply than those that are sold separately from cases. If possible, avoid power supplies with sleeve bearing fans, as these are of considerably lesser quality.

Before purchasing any PSU, make sure that the supplied wattage is sufficient for your components. Power requirements are usually listed in the manuals that came with your components. It is important to note a power supply’s total power, and the power at each voltage: 3.3, 5 and 12V. If any of these do not meet your requirements, the rest of the specifications don’t matter.

Some companies have calculators to help you determine what your power supply needs are; if you are the type to just plug in the numbers without reading the details, you should buy a power supply that is 1.5 to 2 times the wattage that results from these calculators.

For a quiet system, you can choose a fan-less power supply — more expensive but well worth it if noise is a concern, but be sure to monitor system temperatures to make sure cooling is adequate.

For cases and power supply here are some things to consider:

Form Factor
Form factor is the specification that provides the physical measurements for the size of components and where mounting devices for them are located.

  • EATX or Extended ATX boards are 12″x13″. This format is almost exclusive to workstation computers.
  • ATX is the most common form factor and is the de facto standard. In this form factor the motherboard is (usually) vertically mounted for more space and more efficient cooling than some other standards.
  • microATX, or µATX, is smaller than standard ATX, but at the cost of fewer expansion slots. Many cases that support ATX also allow micro-ATX. Flex ATX is even smaller than micro-ATX, but only allows 2 expansion slots.
  • WTX is intended for workstations and servers. Note: WTX has been discontinued as of 2008.
  • BTX is another formfactor designed for more efficient cooling.
    • PicoBTX 8″x10.5″
    • MicroBTX up to 10.4″x10.5″
    • BTX up to 12.8″x10.5″
  • Mini-ITX is even smaller than BTX, at 6.75″ square.
  • NLX

Many OEM computers use non-standard form factors. Be sure to choose a motherboard compatible with your case’s form factor.

The Mini-ITX form factor is much different in important ways unlike its relatives the Micro-ATX and the Flex-ATX. The mainboard size can be up to 170mm x 170 mm which is smaller than the Flex and Micro-ATX can be. Usually at less than 450 watts, the Mini-ITX PSU is energy efficient(but you may not be able to use high power GPU’s and to a lesser extent , CPU’s). The Mini-ITX is also backward-compatible with the Flex/Micro-ATX models.

Number of Storage Drive Spaces
Internal hard drives/floppy drives (which go in the small 3.5″ bays) and internal CD/DVD drives (which go in the large 5.25″ bays) take up space in the case, so make sure you consider how many drives you will need and what size slot they require. Note that optical drives and floppy drives will need what are called “external” slots (meaning they have a hole in the case through which their face can be accessed), while hard drives do not need to be manipulated manually often, so they can usually go into an “internal” slot. This is not to be confused with an external drive, which doesn’t go into the case at all.

Note that it’s possible to buy adapters to fit items that go in small bays (usually hard drives) into large bays. It is, however, not possible to do the reverse.

Power Rating
The power supply unit (PSU) you choose needs to supply enough stable DC power to all the components and even to some of the peripherals. It needs also to be consistent, by complying with accurate standard voltages, i.e. the 12 volt rail needs to supply 12 volts (within normal tolerances of 10% or so) steadily under any foreseeable load, likewise the 3 and 5v rails at their respective voltages. Cheap power supplies tend to fall down in these areas. There are several tech-heavy websites that actually throw a multimeter on the PSU in the course of a review, seek these out and make sure you select a quality PSU.

In selecting a power supply, check carefully that it has the power feeds you need, e.g. six-pin PCI power, 20 vs. 24-pin motherboard connectors, etc. If you are planning on running two or more video cards in SLI (NVIDIA) or Crossfire (AMD) mode, make sure your power supply is approved for that. Both companies have certification programs.

There are several calculators that try to help you select an adequate PSU for your system, such as:


Choose an efficient PSU. Efficient PSUs run cooler and more quietly and thus do not create as much noise (important if you plan to sleep (or think) in the same room with it or use it as a media center PC). They also reduce the wastage on energy.

If your budget allows, consider opting for a modular PSU. These have connectors that can be added or removed, which allows for more versatility and also reduces clutter. The power supply also has an exhaust fan that is responsible for cooling the power supply, as well as providing a hot air exhaust for the entire case. Some power supplies have two fans to promote this effect.

It is important to buy a power supply that can accommodate all of the components involved. Some may argue that it is the most important part of a computer, and therefore it is worth spending the money to get a decent one.

More information about this can be found at Silent PC Review, OCAU Wiki, among others.



A supplemental fan. This one mounts in an unused expansion card slot.

Most cases mount one or more case fans, distinct from the fans that may be attached to the power supply, video card and CPU. The purpose of a case mounted fan is to move air through the system and carry excess heat out. This is why some cases may have two or more fans mounted in a push-pull configuration (one fan pulls cool outside air in, the other pushes hot interior air out). The more air these fans can move, the cooler things will generally be.

Fans for case cooling currently come in two common sizes, 80 mm and 120 mm, and computer cases tend to support one size or the other. The larger 120 mm fans spin more slowly while moving a given volume of air, and slower fans are usually quieter fans, so the 120 mm fans are generally preferred, even though they cost a little more. Good 80 mm fans can still be fairly quiet, so while fan size is a factor, it shouldn’t be a deal-breaker if the case has other features you like.

Make sure the power plug on the chosen case fan is supported by your motherboard; 3- and 4-pin Molex connectors are common. Fans can also be powered directly by the PSU, but in that configuration, the motherboard can’t control or report the fan’s speed.

Variable speed fans with built-in temperature sensing are available, but they may need to be specially ordered from an electronics supply warehouse. They also may not have power plugs attached to their wire leads, but this can be remedied by a competent technician. Variable speed fans tend to run quieter than constant speed fans, as they only move as much air as needed to maintain a set temperature within the case or the power supply box. Under typical operating conditions they may be barely audible.

Since fans run continuously when the computer is turned on, bearing selection may be important for long life. The least expensive fans use sleeve bearings. As the fan ages, the lubricant in the sleeve bearing dries out and eventually the bearing wears, allowing the fan blade to nutate or vibrate, making it very noisy. In severe cases the bearing may seize and the fan will stop turning entirely, possibly jeopardizing the computer when ventilation fails. The most expensive fans tend to be those that use ball bearings, but they also have very long service lives. It isn’t uncommon for a ball bearing fan to run continuously for 7 to 10 years — possibly longer than the useful technological life of the computer within which it is mounted. Ball bearing fans tend to be slightly noisier than sleeve bearing fans. A fairly recent type of fan bearing is a magnetic or “maglev” bearing, which uses a magnetic field to suspend the fan rotor without physical contact. Such fans exhibit practically zero bearing wear and barring a failure in their motor drive components, have essentially an infinite service life. Maglev bearings also tend to be completely silent, and when used in a variable speed fan, can produce practically silent ventilation.

CPU (Processor)
We discuss choosing a CPU in the next chapter, How To Assemble A Desktop PC/Choosing the parts/CPU.



A PC motherboard: IDE connectors and the motherboard power connector (white with large holes) are on the left edge. Between them and the large quadratic CPU socket in the lower middle are the longish RAM sockets. The extension slots are above the CPU socket (two white, one black) and the ports for external devices are on the right edge.

The motherboard is a very important part of your computer. The difference between a cheap and a quality motherboard is typically around $100. A good motherboard allows a modest CPU and RAM to run at maximum efficiency whereas a bad motherboard restricts high-end products to run only at modest levels.

There are six things one must consider in choosing a motherboard: CPU interface, Chipset, IDE or SATA support, Expansion slot interfaces, and other connectors. One must also make sure that the motherboard is of a form factor compatible with the case.

CPU Interface
The CPU interface is the “plug” that your processor goes into. For your processor to physically fit in the motherboard, the interface must be an exact match to your processor. Intel currently has two mainstream formats, the LGA 2011-v3 for their current i7 Extreme/Xeons processors (i7-5820K or i7-59xx) or the LGA 2011 supporting their older (cannot be interchanged)high-end Core i7 39XX and 49xx CPUs (as well as Xeon CPUs for servers), the LGA 1150 for the current generation desktop Core i5 and i7 series, and LGA1155 for the previous generation core i5/i7 processors(Ivy Bridge).AMD currently uses four sockets: AM3+, AM3, FM1, and FM2. The AM3 and AM3+ sockets are compatible with DDR3 RAM. The FM1 and FM2 sockets are used for AMD’s line of A-series APU processors, which are also compatible with DDR3.

Check with the motherboard manufacturer to ensure that the slot on the motherboard will support the CPU you want to use. It is important to know whether the motherboard’s bus can support the exact CPU you plan on using.

If the motherboard, CPU, and heatsink/fan are not compatible and installed correctly, you can destroy the CPU and/or the motherboard in a matter of seconds. Most modern processors come with a stock cooling fan which will work well at stock speeds, stick with this if you have any doubts.

The function of BIOS is highly important. Some BIOS feature crash proof functions essential for updating the firmware. Other motherboards allow BIOS control of overclocking of CPU, RAM and Graphics card which are much more stable and safer for overclocking. Newer BIOS have temperature controls, and functions that shut down the computer if the temperature gets too high.

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The CPU chipset is also important. Some low-end motherboards use cheaper chipsets(low-end). These have limited ports and features.

For instance , take the support of SATA 3 and USB 3 ports. The low-end H81 chipset supports only 2 of these , while the high-end Z97 supports 6 of them.

IDE (ATA) or SATA Interface
Used for connecting hard and optical drives, most motherboards used to have two parallel, 40 pin IDE interface connectors which are now mostly used for backwards compatibility if they are present. These old PATA (parallel ATA) connections have been largely replaced by SATA (Serial ATA) connections for hard drives and optical drives. SATA connections are simple – one plug, one cable, one device.

In the older PATA/IDE standard up to two devices could be connected to each port in a Master/Slave configuration. A 44 wire ribbon cable was used for this connection with three connectors, one on each end and one in the middle (actually slightly off center). One end was plugged into the motherboard connection and the other end plugged into the first (or only) device. If two devices are connected the second is connected to the middle connection. The device plugged into the end must be configured as a master (usually via a jumper on a set of pins on the device) while the second must be configured as a slave – OR both must be configured as “cable select”.

Two devices connected on the same IDE port can contend for access to the bus, causing a reduction in the effective speed of the drives. The newer serial ATA (SATA) interface has four or more separate motherboard connections that allow independent access and can increase the speed at which hard drives work. The cables are also narrower, improving the flow of air inside the case.

The support for older (PATA) IDE drives is starting to disappear. The new G/Q/P 965 chipset series from Intel completely dropped support for such devices. Nevertheless, many motherboard makers are still including an additional IDE controller on their boards, and it still remains possible to buy an extra PCI IDE controller.

Expansion Slot Interfaces


PCI Express slots (from top to bottom: x4, x16, x1 and x16), compared to a traditional 32-bit PCI slot (bottom)

Old motherboards may have one or more the following slots:

  • AGP – for graphics cards (ranging from AGP 1x, 2x, 4x and 8x)
  • PCI – for expansion cards and low-end graphics cards

ATI still manufactures PCI graphics cards, but for better performance try a card supporting PCI-Express. AGP is not a good idea, because it is a standard that is on its way out. You may come upon ancient motherboards with neither AGP nor PCI, but please don’t waste your time trying to reuse them.

Due to the evolution of new graphics cards on the serial PCI-Express Technology, current newer motherboards have the following connections:

  • PCI-Express(Gen 1/2/3) 16x/8x/4x for mainstream graphics cards (PCI Express Gen 1 x16 is 4 times speed of AGP 8x)
  • PCI-Express(Gen 1/2/3) 1x for faster expansion cards (replacing older PCI)
  • PCI for use of old expansion cards (will eventually be phased out)

Older AGP 8x graphics cards are generally being discontinued in favor of PCI-Express 16x, as the speed and efficiency is about 4 times that of the AGP 8x technology. Old PCI cards are either now built into the motherboard (for sound cards, LAN cards, IEEE 1394 firewire and USB 2.0 interfaces) or becoming PCI-Express variants.

Other Connectors


Male USB “A” connector

Universal Serial Bus (USB)
In addition to the USB 2.0 ports provided on the back panel, most motherboards will have connectors for additional ports, either on the front of the case or in a panel that fits where a PCI card might otherwise be connected. USB 2.0 ports (and be sure that your chosen motherboard supports the faster 2.0 standard) are used for connecting various peripherals such as printers, external hard drives etc. USB connectors are also used for connecting MP3 players, some cameras and an assortment of less serious devices like fans, Nerf missile launchers and drink warmers. Given the growing popularity of USB devices, the more ports your motherboard supports, the better.

USB 3.0 ports are now available on the majority of motherboards and they are even faster than USB 2.0 — up to 5 Gbps. Although the majority of keyboards , mice and other such devices use USB2 , almost all HDD’s available now support the USB 3.0 standard as they are much faster under that.USB 3.0 ports are backwards compatible and can be used with USB 1 or 2 devices, although these will not receive the benefit of USB 3.0 speeds.


Subminiature D9-M serial port connector

Serial (COM) or parallel (printer) ports
Use of traditional 25-pin subminiature D parallel printer ports and RS-232 9-pin subminiature D serial ports has been waning since the early 1990s since the introduction of the Universal Serial Bus. Many motherboards no longer offer parallel ports — formerly used almost exclusively for connecting printers — altogether, while serial ports, which once numbered as many as four, are now usually solitary. The principal use for serial ports once was to connect to a mouse or an external modem; both of these devices now connect via USB. Unless you are connecting old peripheral hardware, these ports will be of minimal importance. Even so, USB-to-Parallel and USB-to-Serial adapter cables are available, allowing late model computers to communicate with older peripherals


Firewire connector

IEEE-1394 Firewire
Firewire ports are principally used for connecting DV (Digital Video) cameras and external hard drives. This technology got a foothold because it was much faster than USB 1.0 and 1.1. With the near-ubiquity of USB 2.0, however, Firewire 400, the original, and still the most common IEEE-1394 implementation, was actually a little slower. For this reason, and in spite of the existence of a faster but seldom implemented Firewire 800 specification, Firewire is not as popular as USB. Like USB, most motherboards that support Firewire will have one or more external ports on the back panel and the ability to connect one or more additional ports. One or two Firewire ports will suffice for most users.

Note that, regardless of the motherboard’s native support, additional ports of all kinds can always be added via a PCI or PCI-E 1 expansion card.

The amount of random access memory (RAM) to use has become a fairly simple choice. Unless one is building on a very restricted budget, one just has to choose between installing one, two, four, or eight gigabytes. One gigabyte of RAM is plenty for most modern operating systems, but all of them will run a little faster with two or four gigabytes. While 32-bit operating systems can address 4 gigabytes, they can utilize little more than three gigabytes as system RAM (actually 4 gigabytes minus Video RAM minus overhead for other devices). If one wishes to utilize the full 4 (or more) gigabytes of RAM, one needs to install a 64-bit operating system. It really comes down to a financial decision. One might also choose to get one gigabyte of high quality RAM over two gigabytes of lesser quality, especially if one plans to overclock. Some specialized applications may profit from more than two gigabytes of RAM. If one plans on using such, make sure to check that both the operating system and the motherboard will accommodate the amount of RAM one has in mind.

Another thing to consider when choosing the amount of RAM for one’s system is the graphics card. Most motherboard-integrated graphics chips and PCI Express graphics cards marketed with the “Turbo Cache” feature will use system memory to store information related to rendering graphics; this system memory is generally not available at all to the operating system. On average, these graphics processors will use between 64 megabytes and 512 megabytes of system memory for rendering purposes.

The actual type of RAM one will need depends on the motherboard and chipset one gets. Some old motherboards use DDR (Double Data Rate) RAM or DDR2. DDR3 is the current industry standard. Chip sets that use dual-channel memory require one to use two identical — in terms of size and speed — RAM modules. The RAM should usually operate at the same clock speed as the CPU’s Front Side Bus (FSB). The motherboard may not be able to run RAM slower than the FSB, and using RAM faster than the FSB will simply have it run at the same speed as the FSB. Buying low-latency RAM will help with overclocking the FSB, which can be of use to users who want to get more speed from their systems.

If one is upgrading an existing computer, it is best to check if one’s machine requires specific kinds of RAM. Many computer OEMs, such as Gateway and Hewlett-Packard, require custom RAM, and generic RAM available from most computer stores may cause compatibility problems in such systems.

Labeling of RAM
RAM is labeled by its memory size in megabytes (MB) and clock speed (or bandwidth).

SDRAM (Synchronous Dynamic RAM) is labeled by its clock speed in megahertz (MHz). For example, PC133 RAM runs at 133 MHz. SDRAM is nearly obsolete, as nearly all motherboards have withdrawn support for SDRAM. It is now superseded by the more efficient DDR RAM.

  • 128MB SD-133 = 128MB PC133 RAM

DDR RAM can be labeled in two different ways. It can be labeled by approximate bandwidth; as an example, 400MHz-effective DDR RAM has approximately 3.2 GB/s of bandwidth, so it is commonly labeled as PC3200. It can also be labeled by its effective clock speed; 400 MHz effective DDR RAM is also known as DDR-400. There is also DDR and DDR2 labeled as PC and PC2.

  • 256MB DDR-400 = 256MB PC 3200 RAM
  • 256MB DDR2-400 = 256MB PC2 3200 RAM

DDR RAM has 4 versions: DDR (also DDRI), DDR2 (or DDRII) , DDR3 and DDR4

  • DDR supports DDR-200, DDR-266, DDR-333, DDR-400 (mainstream) and DDR-533 (rare)
  • DDR2 supports DDR-400, DDR-533, DDR-667, DDR-800, DDR-1066
  • DDR3 supports DDR-1333 to DDR-3000

Hard Drive and SSD


A hard drive

Things to consider when shopping for a hard drive or SSD:

The interface of a drive is how the hard drive communicates with the rest of the computer. The following hard drive interfaces are available:

  • Parallel IDE drives (PATA, also known as ATA or IDE) use cables that can be distinguished by their wide 40-pin connector, colored first-pin wire, and usually gray “ribbon” style cables. This technology is largely obsolete because SATA uses thinner cables, eliminates contention for the IDE bus that can occur when two PATA drives are attached to the same connector, and promises faster drive access. SSD’s are generally not available for IDE , as they are too slow for a SSD(one notable exception is Transcand as of November 2014).
  • SATA drives have the advantages outlined above. If you want Serial ATA, you will either need to purchase a motherboard that supports it (all newer motherboards do), or purchase a PCI card that will allow you to connect your hard drive. Note that some older motherboards will not allow you to install Windows XP to a Serial ATA hard drive. There are 3 types of SATA. SATA 1 provides up to about 150 MB/s , SATA 2 provides about 300MB/s , SATA3 provides up to about 600 MB/s. Most new computers and HDD’s come in SATA 3 , but older computers may use SATA 2/1. Although they are both backwards and forward comparable , SSD’s should be used in SATA 3 since they are too fast for SATA 2 or 1.
  • SCSI, although more expensive and less user friendly, is usually worthwile on high performance workstations and servers. Few consumer desktop motherboards built today support SCSI, and when building a new computer, the work needed to implement SCSI may be outweighed by the relative simplicity and performance of IDE and SATA. SCSI hard drives typically reach rotational speeds of up to 15,000 RPM, and are more expensive.
  • USB can be used for connecting external drives. An external drive enclosure can convert an internal drive to an external drive.
  • IEEE1394 This format is most commonly known as “Firewire” (Apple) or “I link” from Sony. The theoretical speed of IEEE1394 is double that of USB 1.0.
  • PCI-E uses the PCI lanes of your computer. These lanes can be used to connect premium SSD’s , and they are much faster than SATA-based SSD’s.

SSD is a hard storage systems that use flash memory rather than rotational platters. Because of this , they make virtually no noise and generate far lesser heat than a HDD. If you plan to upgrade a computer , it is an excellent idea to replace an HDD with an SSD as the performance of the computer can be boosted by a wide margin. However , there are some important drawbacks.

  1. They are significantly more expensive than a comparable HDD.
  2. SSD sizes top out at about 2 terabytes , while comparably , for HDD , it is about 8 TB.
  3. They cannot last forever. The majority of SSD’s use NAND cells , which will wear about after a certain amount of writes. However , this problem is mitigated to a lot of extent by using technologies so that all cells wear out at the same time. Also , good SSD’s have huge data life (150 TB) and high warranty period(10 years).

There are some important precautions to note if you do buy a SSD.

  1. Do not defragment the drive! SSD , unlike HDD , does not need to get defragmented and will instead cause unnecessary writes and can wear out the drive faster. If you do use a SSD in a Windows OS before Windows 7 , make sure to disable automatic disk defragging. Windows 8 already identifies the drive and makes necessary optimizations.
  2. Use SATA 3. As outlined above , using SATA 2 or below reduces speed. If you can afford it , go for a PCI-E SSD as they are faster.
The cache of a Hard drive is a faster media than the hard drive itself and is normally 8MB (low end and laptop drives), 16MB, 32MB (standard desktop drives), or 64MB (high end, high capacity desktop drives). The existence of a cache increases the speeds of retrieving short bursts of information, and also allows pre-fetching of data. Larger cache sizes generally result in faster data access.
Form factor
  • 3.5 inch drives are usually used in desktops.
  • 2.5 inch drives are usually used in laptops.

A 2.5 inch disk can be used in desktops using adapters , but not vice-versa.

The smallest desktop drives that are widely available hold about 160 gig of data, although the largest drives available on the market can contain 6TB (6072GB). Note that the advertised capacity is usually more than the actual size. Few people will need disks this large – for most people, somewhere in the range of 300-750GB will be sufficient. The amount of space you will need can depend on many factors, such as how many high-end games and programs you want to install, how many media files you wish to store, or how many high-quality videos you want to render. It is usually better to get a hard drive with a capacity larger than you anticipate using, in case you need more in the future. If you run out of space, you can always add an additional hard drive using any free IDE or Serial ATA connector, or through an external interface, such as USB or FireWire.
Rotational Speed 
The speed at which the hard drives platters spin. Most laptop (2.5 inch) drives spin at 5400 RPM, while common desktop drives come in at 7200. There are PATA and SATA drives that spin at 10,000 RPM and some SCSI drives hit 15,000. However drives above 7,200 RPM usually have limited capacity, and a much higher price than comparable 7,200RPM drives, making such drives advisable only when the fastest possible speeds are required. SSD’s do not have rotational components.
Noise and Heat 
Modern hard drives are fairly quiet in operation though some people are sensitive to the faint hum and occasional buzz they do make. If your HDD is loud, it’s time to think about replacing it. Hard drives will also throw some heat and adequate air circulation should be provided, usually by case fans. There is software available that will allow you to monitor both the health and temperature of your hard drive(s), it’s a good idea to check from time to time. SSD’s do not generate noise and heat as HDD does because they have no rotational parts.
Many manufactures offer warranties ranging from 30 days (typically OEM) up to five years. It is well worth spending an extra few dollars to get the drive that carries a longer warranty. Good quality SSD can provide up to 10 years warranty(like Samsung 850 Pro).

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