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Building your own PC is actually simpler than it sounds. No longer, if ever, are the days of working with a soldering iron, a box of resistors, and a hand drawn circuit diagram with tea cup rings on it. PC parts come in modular components, and it is simply a matter of deciding on the performance and functionality you want your PC to have, selecting the appropriate and compatible parts, and putting it together.

This page starts with a quick introduction to the main parts of a PC and the general acronyms used. It then follows with a detailed description of each of the main components you will need to buy. Each of these descriptions contains a full tick list of the specifications and features to be considered, and how to ensure compatibility and maximum performance between each component.

The second page, “PC Assembly” gives a final summary table of the components you need and the specifications to check, followed by a tick list of the simple steps required to assemble the PC. Finally there is a quick description for the installation of the required software components including the motherboard BIOS, Operating System, and hardware drivers.

The main components of a PC  (fig 1)

Parts of a Computer

The Case

The case is used to house your PC components. It consists of a frame and covering panels to protect the internals of the PC; a chassis on which to fix the PC motherboard, power supply, and internal drives; an I/O panel for giving external access to the motherboard I/O connectors, a front panel providing a power button and indicators, and mountings for attaching cooling fans to provide an air flow.


The motherboard is the main component inside the case. It is a large rectangular printed circuit board with integrated circuitry and sockets that connect all of the other parts of the computer together. These other parts include the processor, memory (RAM), the disk drives (hard disk, CD/DVD/Blu-Ray drive), peripherals, and any expansion cards (video, network, audio, tv etc). The motherboard also offers an I/O panel to the rear of the PC case for plugging in your peripherals and external devices (e.g. monitor, keyboard, mouse, speakers, and others). Many motherboards also include integrated network and audio chipsets so you don't need to buy and fit separate expansion cards.


The processor or CPU (Central Processing Unit) as its name implies, performs the majority of the processing (calculations) which enable a computer to function. Most modern processors include a simple Graphics Processing Unit (GPU), although for higher end graphics and gaming PCs you will usually want to install a dedicated graphics (video) card expansion. The CPU generates a lot of heat when running, so is usually connected to a heat sink and fan for cooling.


The memory or RAM (Random Access Memory) is used to store the data and code that are currently and actively being used (accessed) by the CPU. Because a hard disk drive uses magnetic storage technologies (a bit like a tape cassette) and requires the movement of a physical head to access the different parts of its memory storage, it is hundreds of times slower than RAM, which stores it's data in electrically charged transistors, any one of which can be instantly accessed using binary addressing. So in order to vastly increase a PCs speed and response times, when you open an application or file, the program code and file data are loaded from the hard drive and stored locally in RAM for quick access. RAM is a form of "volatile" memory, this means that when you turn off the power to your PC all of the data stored in RAM discharged and is lost.

Hard Drive

The hard disk or HDD (Hard Disk Drive) is "non-volatile" memory. This means that it remembers all data stored on it even when the power is turned off. Because of this, it is used for all permanent internal data storage including the Operating System, all installed programs, and your saved files. Whenever you install a program or save a file, it is written to the hard drive.

Optical Drive

The optical drive is your CD/DVD (or now Blu-Ray) disk drive, and is used for reading or writing large amounts of data between the CD/DVD disk and your computer (e.g. installing 3rd party applications or playing multimedia files such as films or music).

Power Supply Unit

The Power Supply Unit (PSU) is used to convert the mains 240V 50Hz AC electricity power supply into the low-voltage DC power required by the internal components of the computer.

Expansion Cards

Sometimes for high end or special purpose PCs, you may want to install expansion cards that provide additional functionality or performance. These cards have hardware or processors dedicated to handling specific tasks at high speed. The most common of these are graphics, network, audio, and tv expansion cards.


Peripherals are the additional external components that you plug into your PC. The main peripherals are your monitor, keyboard, mouse, and speakers.

Processor Support

Motherboards are generally designed for a specific processor family (i.e. as prescribed by the fitted processor socket), and so as a starting point should be fairly well matched to the speed and performance requirements of the processor. The motherboard BIOS automatically recognises the processor model and will set any default clock speeds (or any overclocking settings if overclocking your PC).

Maximum processor performance can however be compromised by not choosing a motherboard and  RAM modules that support the maximum memory type listed in the processor specifications (i.e. channel support and memory/bus speed, e.g. dual-channel DDR3-1600).

Many processors nowadays also have advanced technologies such as dynamic overclocking functionality (where the processor can automatically increase or decrease it's processing (clock) speed during times of heavy or light usage). If you want to make use of these, make sure that the motherboard also supports these processor technologies.


The North and South Bridge chipsets (often referred to as simply the chipset) manage data transfer between the CPU and peripherals (i.e. RAM, PCI expansion cards, hard and optical drives etc.) and come as an integrated part of the motherboard. Processors will specify a set of compatible chipsets, and for a standard user these motherboard chipsets will be matched to the processors requirements and performance. But if you are building a high-performance PC, some of the higher-end chipsets have slightly improved feature sets, such as more PCI expansion card or USB lanes (busses) to avoid congestion if using numerous transfer intensive peripherals.

If you want to check the chipset specifications, you should also note the USB/PCIe versions supported by the processor and chipset (for example if you want to use newer/faster USB/PCI v3.0 components), and the supported advanced technologies. Although this information will usually be listed in the motherboard features and specifications.

Bus Bandwidths

A bus is equivalent to a cable that connects two pieces of electrical equipment for transferring data. The difference being that it is integrated into the processor/chipset silicon or motherboard PCB (Printed Circuit Board) and is used to transfer data from one piece of silicon to another at the pervading clock speed. Busses also have a width (e.g. 16, 32, or 64-bits). This means that the bus can transfer 16/32/64 bits of data in parallel (simultaneously), enabling the transfer an entire word of data in a single clock cycle.

Although there are dozens of busses on a motherboard, the main busses to look out for when choosing your motherboard are the FSB and the memory bus to ensure that they match the processor and memory you have chosen to go for (bus speeds are now also specified in GTs (Transfers per second), which does not include the bus width (word size)). This being said, you should note that many motherboards now don't explicitly specify these bus speeds, as they are implied by the processor/chipset and RAM supported by the motherboard.

Bus Bandwidth =  clock speed *1 x  bus width

( *1 clock speed = 1 / clock frequency )

e.g.   66us x 32-bits = 266 MBps

The first question to ask when building your own computer, is to decide what you will want to use it for. Whether you will be using it for simple word processing and internet connection, playing films and music, processing intensive work (such as music or video editing, CAD, or software development), or high-end gaming. The second question is the form factor that you want to use (i.e. the size and shape of the case): ATX Tower (standard PC form), ATX mini-tower, desktop (flat case with a low profile), or laptop.

Once you have decided these two things you can start considering the components you want to buy...

- How to Build your own Computer -


The main parts of a motherboard comprise of the processor socket, the Northbridge/Southbridge chipsets, the Front Side and Memory Busses, the RAM and PCI expansion card connector sockets, the internal and external peripheral device connectors, and any expansion chipsets (i.e. network, audio etc).

A picture of a motherboard  (fig 2)

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A motherboard will offer a selection of connectors for attaching secondary internal components (see images):

It will also offer a selection of connectors for attaching external peripheral components (see images).

Choosing your motherboard

The two most important questions to ask when choosing your motherboard are which processor family and what type of RAM you want to use. After deciding on the processor and RAM you want to go for, the next set of points to consider in choosing the motherboard you want to go for are:

This is the main point at which you will have to do some reading up and shopping about. Read the Processor and RAM sections of this page, then go to a few OEM (Original Equipment Manufacturer) websites to get an idea for the products available. These sites are helpful as they give full feature and performance specifications for their products and you can make direct comparisons between what is out there.

Finally, go to a few PC forum and review sites (listed at the end of this page), read some of the latest reviews and ask some questions on the forums about what people would recommend. They are usually very friendly, willing to help, and can give you some really good information on what you should be looking for. There will be lots of other people who have already asked the same questions, so just read a few posts and you should get up to speed very quickly. It should only take a day or two to start homing in on the combination that you are looking for.

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A motherboard block diagram  (fig 3)


The processor is the central brain of the computer. It is where all of the operating system and software code is run. It also controls access to the hard drive, RAM, and other peripherals. Software applications comprise of lines of code (instructions) that are then computed by performing thousands of basic arithmetical and logical operations, so the faster your processor, the faster your PC.

Multi-Core Processors & Hyper-Threads

Processors used to comprise of a single core, or processing unit that handled all of the computers processing. As clock speeds started to reach the upper limits for current silicon technologies, and computers started to be used more and more for multi-tasking and running numerous applications at once, processor design moved towards multi-core designs. For example, a Dual Core has two processors on a single chip and Quad core has four. Eight and twelve core processors are not far behind.

Multi-core processors are much faster, provided that the software supports them. For example, Windows XP and Windows 7 support multi-core processors, but Half-Life 2 does not. On a single core processor, when running multiple applications, the processor has to perform what is called context switching. This means that when multiple software applications are running at the same time (for example if you are doing some word processing, while downloading a web page, and listening to music, as well as the Operating System running background services), the processor will have to continuously swap between these applications to make it seem that they are running simultaneously. Each time, the processor has to save and flush all of the data currently in the CPU registers for the current application, then load the data for the next application. If you consider this can happen hundreds or thousands of times per second, you can see how this can significantly slow down an application. Multi-core designs can genuinely multi-task by running each application on a separate core, reducing the need for context switching. You will notice a big difference when multi-tasking with the PC being far smoother and more responsive.

Intel have also introduced hyper-threading technology into their processor designs, the theory is that each processor on the silicon has a set of the above mentioned CPU registers for each hyper-thread that is supported. This means there is very little context switching cost as these registers don't have to be flushed and reloaded as often. Tests have shown that hyper-threading can give a 5 to 30% performance increase to the processor depending on the applications running.

Clock Speed

The clock speed of a processor relates directly to how many calculations it can perform per a second. The faster the clock speed, the faster your PC.


Cache is equivalent to super-fast RAM that is incorporated into the processor silicon for fast calculation access speeds without having to access the RAM. Although cache is very important, it is also very expensive as processor silicon space is limited. It seems from tests that upgrading your processors cache size from the standard offering to expensive super-sized cache versions only gives fairly minimal performance increases.

Celerons and Semprons

These processors are special low power chips for laptops.


Processors produce a lot of heat when running and need to be cooled. To do this, they need a heat sink with an attached fan. The heat sink (which works much like a radiator, taking the heat from the processor and transferring it to the air) is pasted directly onto the top of the processor using heat conducting paste, and the fan then attached to the heat sink to keep a continuous flow of cooling air. The more powerful the processor, the more energy it uses and heat it will produce. This means that you will need a more powerful power supply unit, heat sink, and fan. Some PCs even have liquid cooling systems and a heat sink and fan for the Northbridge. If you buy your processor in retail marketing packaging a heatsink and fan will be included. If you buy an OEM  (Original Equipment Manufacturer) version it won't, and you will have to buy a heatsink separately that is rated for the processor clock speed and fits the socket.

Processor Evolutions

The two main pc processor manufacturers are Intel and AMD. Both make excellent processors, but have very different architectures so direct comparisons are hard to make. You should read up on the latest processor versions and performance reviews.

Choosing your Processor

When choosing your processor, it's a good idea not to go for the very latest and fastest, as these can be very expensive at first, and come down in price quickly. You will usually find that if you go for a top end processor that has been around a little bit longer, you will still get excellent performance and it will be a lot cheaper.

* On some multi-core processors stated cache is per core.

Try http://forums.overclockers.co.uk, they have a really good forum and know what they are talking about, and also have an online components shop. They even have pre-posted suggested component lists for PCs in different price and performance brackets. Also try www.extremetech.com for processor tests, and www.intel.com/products/chipsets for information on Intel chipsets.

Memory (RAM)

In many applications, overall speed is governed more by the RAM available and the FSB speed than by the processor itself. If an application is running very slowly, the chances are that you have insufficient memory. RAM comes in modules that fit into dedicated slots on the motherboard.

Current PC RAM modules are of type DDR (Double Data Rate). This means that they can internally access their data twice every clock cycle (once on the up and once on the down tick). DDR2 (Dual DDR) can double internal access speeds again to access data 4 times every clock cycle, and the latest DDR3 can access data at 8 times clock frequency. Due to this, each generation of DDR has been able to approximately double available memory bandwidth.

Dual and Triple Channel Memory

Some motherboards and processors also support dual-channel memory, this again doubles the memory bandwidth available to the processor (over and above that offered by the DDRx RAM module). It can do this by running two RAM modules in parallel and accessing them simultaneously using two memory controllers. To make use of dual-channel memory, both the processor and motherboard must support it, and you must install two identical RAM modules in the correct slots as specified in the motherboard user manual, otherwise this functionality will not work. Intel socket 1366 supports triple-channel memory.

Memory Bus Bandwidth

The memory bus bandwidth states the number of bytes of data that can be transferred per second from a RAM module to the processor, and is calculated as follows:

Bus Bandwidth (MBps)  =  Clock Speed (MHz)  x  Data Width (bits)  /  8  (*2)

( *2 Divide by 8 to convert from bits to Bytes )

e.g:   DDR3 1600MHz  =>  1600 MHz  x  64 bits / 8  = 12,800 MBps bandwidth

Note: The above doesn’t include the effect of dual/triple channel memory, and the clock speed used is the stated operating speed of the memory bus/RAM module after any DDRx multipliers (see below). As memory busses are also Dual Data Rate, the stated bus speed is actually twice that of the clock frequency used. Also today RAM and FSB are all 64 bit.

The above memory example would be labelled “PC3-12800 DDR3-1600”, and if two of these modules were used in dual-channel configuration, you will achieve an overall memory bandwidth of 25,600MBps!

RAM Module Labelling

To make it easier to find the memory you are looking for, RAM memory modules have the following labelling system:

DDR3 PC3-12800 1600MHz     or     PC3-12800 DDR3-1600

DDRy-xxxx:  Denotes the memory DDR type (y), and it's operating clock speed (xxxx) in MHz - note, this is the memory clock speed after the DDRx clock multipliers have been applied, and is the value to be matched to the supported memory stated by the motherboard and processor (so in the example above, DDR3 that operates at a clock speed of 1600MHz).

PCy-zzzzz:  Denotes the memory DDR type again (y), and the memories maximum transfer rate (zzzzz) in MBps (see formula above), this is the value that has to match the motherboards memory bus bandwidth.

It is also worth noting that many memory modules also state a CLx value. CL is the CAS Latency that states the number of clock cycles it takes the memory to return a requested piece of data. The lower the CL the better, as although two memory modules may run at the same clock speed, if one has a CL of 5, and the other a CL of 9, the CL5 memory will return data 4 clock cycles sooner than the CL9 memory. Although it is always worth buying RAM with the lower CL, if it is significantly more expensive the performance increase probably won't justify the increase in cost. From tests, it seems that a decrease of 2 in the CL provides approximately a 3% increase in performance. For most users a CL of around 7 to 9 is amply good enough - CL timings usually range from around 5 to 11.

Below is a table of available RAM types, and their specifications:

Choosing your RAM

Motherboards generally only support one type of DDRx RAM, although it may support multiple speeds, and this information will be given in the motherboard and processor specifications. You should generally go for the fastest memory that the motherboard and processor support, with a good CL latency. Nowadays you don't have to worry about the motherboards memory bus speed and bandwidth vs the memory modules stated bandwidth (e.g. 12,800MHz vs PC3-12800), and in fact many motherboards don't even list this information in their specifications. Most motherboards and processors now simply state the memory types that they support (e.g. DDR3-1600/1333), and the memory bus will simply be matched to support this.

Note:   Try www.crucial.com/uk that has a memory advisor, or www.hardwaresecrets.com that has lots of good information on the ins and outs of hardware components, specifications, and performance.

Advanced Stuff

The above sections will let you find the RAM that you are looking for to match your motherboard and processor, but if you want to get confused, here is some more detailed information on RAM modules.

Note: Just to be aware, when talking about the memory and memory bus, there are two clocks. One is the clock that is fed to the memory module, and the second is the clock that is fed to the memory bus (both are generated by the memory controller on the motherboard). The memory bus also operates at Double Data Rate (transferring data on the up and the down tick), but with the introduction of DDR2/DDR3, the memory bus clock has to be increased to twice/four times that of the clock fed to the RAM module in order to match the memories multipliers and available transfer rate.

Note: As a quick note, the values stated in the RAM module specifications are actually the maximum guaranteed clock speed and bandwidth that it will support (as the speed that the memory and memory bus run at are set by the motherboard memory clock generator). This is set automatically by the motherboard BIOS when it checks the installed memory type, but can be manually over or under clocked.

Memory timings: When buying memory, it may also state it's performance timings, for example  5-5-5-15 or 9-9-9-24. These numbers indicate how long it takes the memory to perform certain operations, and have the associated labels: CL-tRCD-tRP-tRAS-CMD. These timings are by default set automatically by the motherboard BIOS, but can be changed manually to improve performance if over-clocking. www.hardwaresecrets.com has a good article on "Understanding RAM timings".

Some other memory features that may be stated are:

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Hard Disk Drive

The Hard Disk Drive (HDD) holds all permanent internal data storage for your PC (i.e. the Operating System, installed programs, and your saved files) using magnetic storage technologies and requires the movement of a physical head to access the different parts of its memory storage.

You will need a hard disk with a decent amount of space, at least 400GB, although affordable hard disks now go up to 2TB (Hard disk drives usually cost about 50p per GB). For an example of data usage, a single high quality MP3 song uses approximately 8MB, a relatively decent game 5GB to 10GB, and 1 hour of camcorder footage uses approximately 13GB.

Other important performance specifications that may or may not be listed in the hard disk description are it's Sustained Transfer Rate, and it's seek time. Sustained Transfer Rate is just as important as the hard drives interface bandwidth and indicates how quickly the drive can read data from it's own disk, so this is the real bottleneck for apparent hard disk speed. Sustained transfer rates currently peak at approximately the 100MBps mark, but can go up to 200MBps with drives that have multiple heads and internal disks.

Seek time is also an important metric, and is the amount of time it takes the disks head to move to the required part of the disk for reading or writing. Average seek times currently sit at around 8.5ms. This information should usually be found in the hard drive manufacturers specification document.


Nowadays all hard disks use SATA connectors. Previous to SATA, various versions of IDE were used. SATA is very simple, you use one drive per cable (channel) that connects directly to the motherboard. IDE uses a flat and very wide 40-conductor ribbon cable. You can also use an 80-conductor cable (with the same plugs as the 40-conductor, but twice the wires in the ribbon) that enables 2 drives to use the same ribbon cable, one master and one slave, set with jumpers in the cable select.

Choosing your Hard Drive

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The Case

All motherboards and cases adhere to a set of industry standards for their dimensions. You can choose to go for a Tower or a Desktop case (tall of flat). The Tower (ATX form factor) is the most common and recommended as it is prevalent and easier to work with. Towers come in Full, Mid, and Mini sizes, although smaller sizes will have less room for extra cards and drives.

Cases may have all in one or separate removable side panels, use screws or clips, have a removable internal motherboard tray (easier to install), or have a cable stowing compartment to keep the inside of the case clutter free. The case will also have a number of fan grills and mountings for ingress and egress of air flow. The case will also need several 5.25" external drive bays for optical disk drives and other front panel devices, and several internal 3.5" drive bays for hard disk drives. The external drive bays will have a removable cover for installation and access.

Choosing your case

Case designs range from the boring to funky, plastic to pressed steel or brushed aluminium. Some are lightweight, others are reinforced. But remember, functionality before frills!

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Power Supply Unit

The power supply unit supplies power to the motherboard, drives, and other components in the PC. It has a standard 3-pin mains power cable and connector for plugging your PC into the mains electricity supply, and a power cable internally to the case that has numerous different power connectors coming from it to power the various internal PC components (see images). Some cases come with a PSU pre-installed, but it is recommended to buy your case and PSU separately as you will then be able to match the PSU to the power requirements of your installed components. Power supply units also conform to industry standard dimensions, so for an ATX case, you would need to buy an ATX power supply unit.

* Adapters can be found to convert most of these connectors if necessary.

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Optical Drive

Optical drives are your standard CD, DVD, or Blu-Ray disk drive used for reading or writing large quantities of data to and from your PC. Newer optical disk types are backward compatible for reading data (i.e. a Blu-ray drive will read DVDs and CDs, and a DVD drive will read CDs). But this is not necessarily true for writing to disk, so you should check the optical drives specifications for compatibility.

Optical disk drives use the same interface (connectors and cables) as hard disks, so it is preferable to go for a drive with a SATA connector. Some also come with around 2 to 4MB of buffer memory to smooth out any delays or jitter in the read write bus. Don't worry too much about the drive speed, most are plenty fast enough, and can go at up to 16x speed. But be careful when writing data to disks, as if you set the write speed multiplier too high, the PC may not be able to keep the write buffers full, resulting in a write fail.

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Graphics Card

The graphics or video card, is an expansion card that you can add to your PC to increase graphics performance. A graphics card has a dedicated Graphics Processing Unit (GPU) and RAM, and is a mini-computer in itself. Although graphics cards are packaged and made available by numerous companies, the core graphics chipsets they use are made by NVidia or ATI (AMD).

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Try www.tomshardware.co.uk/graphics that has a graphics card advisor.

Sound Card

When deciding whether you want to install a sound card, ask the questions, do I want to play music, play games, watch films, and/or record music from connected instruments. Your decision will also depend on the motherboard you choose. Many motherboards have excellent integrated multi-channel surround sound chips that rival expansion cards (look for a motherboard with integrated AC'97, HDA, Realtek ALC880), also check that it has the full set of audio connectors on it's I/O panel. It is generally recommended to go with integrated audio to start with unless you have particular audio needs.

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Network Card

The Network Interface Card (NIC) is the interface between your PC and the internet or any other connected network, for example a Local Area Network (LAN). The NIC links your PC to a router, external modem, other PC, or external devices via LAN. The standard option for a NIC is to support Ethernet (Standard, Fast, or Gigabit - 10/100/1000Gbps). You can also get 10/100/1000 BASE-T, or Dual/Triple Speed Ethernet PCI cards. Again, most motherboards have very good integrated NIC chips, check that it has an RJ45 (Ethernet cable) connector on the I/O panel. So once again, unless you have specific needs, it is recommended to go for a motherboard with an integrated NIC.


You can use WiFi to connect your PC to the internet or LAN wirelessly without using cables (wireless Ethernet). Most laptops come with integrated WiFi, you can also buy plug-in USB WiFi dongles that come with their own installation software, or buy a WiFi expansion card. The 3 WiFi standards are shown below. It is recommended to go for 8702.11g, as this is fairly standard and is 802.11b and 802.11g cross compatible.




Note: If you go for a USB keyboard, it may be worth keeping a PS/2 keyboard available somewhere, as some motherboards will not pick up USB keyboard input before being configured to do so.



Other peripherals

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Other Accessories


Before broadband, dial-up connections were used to connect your PC to the internet using existing phone lines. Standard modems have a maximum speed of 56kbps over a single phone line due to the bandwidth limitations used in standard telephone lines, although some hardware and server-side compression technologies can increase this to 320kbps or even 1Mbps.


FireWire (IEEE-1394) is a high speed connector for transferring data between a PC and external devices. Although there are differences between USB and FireWire for advanced users, for most, the two have similar transfer rates. But it may be worth having a FireWire socket in case you want to use an external device that has a FireWire port.


Bluetooth was the pre-WiFi standard for connecting devices wirelessly, although it has become less common for use with PCs, it is still fairly common in mobile and consumer electronics devices.

Front Panel Bay Devices

You can also install front panel bay devices to customise your PC. There are a wide range of products available including fan controllers that display internal temperatures and fan speeds allowing you to adjust fan speed control settings, audio controllers that give you play controls and display a graphic equaliser, and port hubs that allow you to add additional connector sockets to the front of your PC including additional USB connectors, FireWire, and Media Card readers.

- Part 1: Components -