Unlike most other electronic devices and appliances, PCs retain an air of mystery. The functions of the monitor, keyboard, mouse and loudspeakers are all fairly obvious, but the big cream-coloured box or ‘system unit’ -- which they all plug in to -- gives little away. It’s not necessary to understand how a PC works in order to use one, but it helps to know a bit about what’s inside. Sooner or later you will want to remove the lid, to carry out an upgrade, add extra functionality, or try to find out why it has stopped working...

The heart of any PC is the motherboard. This large printed circuit board, mounted on the side or the bottom of the case, contains the central processor unit (CPU) chip, (386, 486 Pentium etc.), plus all of the support systems for the CPU and the other components inside the case. The CPU is the biggest chip on the board, often fitted with a finned metal heat-sink and miniature cooling fan. CPUs are mounted in a clamp or ‘ZIF’ socket, so they can be easily removed. The next most important part of the motherboard are the rows of memory sockets, some or all of them will be populated with memory boards. These are small strips, a couple of centimetres wide, with RAM chips on one or both sides. They come in several different sizes and capacities (1, 4, 8, 16, 32 and 64 megabytes). The most common size is the 72-pin SIMMs. Some older machines have slots for 30-pin SIMMs, or a combination of 30 and 72-pin types; newer PCs mostly use 168-pin DIMMs.

Motherboards have a number of ‘daughter-boards’ that plug into rows of sockets or ‘expansion slots’. These may include the graphics card, that processes the video output for the monitor, a sound card, connected to the speakers, controller cards for disc drives and other external devices and possibly an internal modem. Recent motherboards may have some or all of these functions built-in. There are a number of different types of expansion slot, most PCs have a mixture of EISA/ISA and PCI sockets. When adding a new card it’s important to make sure there’s a vacant slot of the correct type. 

The majority of PCs have three disc drives, assigned identification letters by the operating system. Drives ‘A’ and ‘B’ are used by removable floppy discs; drive A is for 3.5-inch types, ‘B’ drives are quite rare nowadays, they were used for older 5.25-inch diskettes. Drive C is the main fixed hard disc drive, that stores the PC’s operating system and applications software. Drive D is normally the CD-ROM deck.

The power supply module is housed in a metal case with a built-in cooling fan. All PCs have an internal speaker, that emits diagnostic bleeps during the boot-up sequence. 

On the backside of a PC you will find a collection of plugs and sockets or ‘ports’. There are normally two serial communication ports, ‘COM 1’ -- a small round socket or 9-pin connector -- is generally used by the mouse. COM 2 (9 or 25-pins) connects to external devices, like a modem or digital camera. The 25-pin parallel port, designated LPT 1, is used by the printer and shared with other peripherals, such as scanners and external disc drives. The monitor cable also plugs into a 9-pin socket, on the back of the graphics card. A deeply recessed round socket is for the keyboard and there may be several jack sockets, for the loudspeakers and a microphone. Although plugs and sockets are not always marked, it should be clear where each cable goes, and impossible -- in theory -- to mix them up...



The right mouse button in Windows 95 has many hidden talents, here’s a few to be getting on with. If you’ve got a lot of open windows and you want to get to the desktop, simply right click on the taskbar. This brings up a menu for minimising, tiling or cascading all windows; right click on the taskbar a second time to restore the windows. A right click on the recycle bin gives the option to empty it straight away. Discs can be quickly formatted by right-clicking on the disc drive icon in My Computer or Explorer.

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