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Computer System

These pages are basic information about IBM compatible computers.

A computer does three things. It takes in data, it processes data and it puts out data. Commonly, a computer takes in data from the keyboard, the mouse, the disk drives, and modem. It processes the data on its motherboard and within its processor. Output goes to the monitor for display, printers for hard copy, disk drives for storage, to the modem for transmission and to other devices for control functions. These are just a few examples.


This picture shows the front of a mini-tower IBM compatible computer. At the front there are (top to bottom by layer) a 3 1/2 inch floppy drive, a 5 1/4 inch floppy drive, a CD-ROM drive, two blank 3 1/2 inch device slots, the power button and (left to right) the reset switch, turbo switch, and the keylock. The computer case is the chassis containing the computer devices and power supply.

Disk drive media refers to the things that you put inside of a disk drive to record data. Hard drives have magnetic metal oxides deposited on rigid metal disks for recording data. Floppy disks use a flexible vinyl surface covered in magnetic oxides. Disk drives are called non-volatile storage. Information stored on a disk drive remains when the computer shuts down. CD-ROMs record data by etching data onto vinyl disk media. A laser scans across the disk surface and produces reflections that are read by a detector. These reflections can be read by a CD-ROM drive but a only very expensive CD-ROM drives can record data.

The power button turns on and off the computer. A LED (Light Emitting Diode) connected by wires to the motherboard lights up when power is on.

Many people prefer using a protected power strip or Uninterruptable Power Supply(UPS) to turn all of their computer equipment on and off conveniently with one switch. While some monitors get power by a plug on the back of a computer, most have their own plugs. Power strips have one cord that attaches to the wall, several outlets, usually its own breaker or fuse and a single ON/OFF switch.

Hard drive access is indicated by a LED next to the power and turbo LED's in most computers.

The reset button restarts your computer. It momentarily disconnects power, causing the computer to reboot. Locked up computers happen, preventing the keyboard, mouse and even Ctrl-Alt-Delete from working. In these situations, the reset button may be of use.

Many older computers allowed the option of doubling or halving the processor clock speed. Games designed for older machines might run too quickly on a new machine. Switching to the slower mode makes these games slower and more playable. Switching back makes your other applications run faster. There is usually a Turbo LED that shows when Turbo is selected. It attaches by wires to a connector on the motherboard. Some fancy LED arrays can be made to show processor speed.

Preventing others from using your computer is possible by use of the keylock. It keeps the keyboard from working. Again, it makes a connection to the motherboard by a wire. If the wire is disconnected from the motherboard, the keylock is useless and the keyboard is always enabled. Many find this desireable.

The back of the computer typically has a minimum of seven connectors. Power in and a monitor power connection are part of the power supply. Your keyboard's round plug normally connects directly into a round plug in your mother board. Align it using the groove dent. The serial, parallel, and game ports are DB type connectors that connect to your mouse, printer and joystick respectively. Your monitor connects into video port on your video card.

Computer back

The wonderful thing about these connections is that, in a basic system, no connector will fit where it doesn't belong! On a properly built computer, all DB connectors on the back of your computer will face the same direction as a capital D when the motherboard is lying flat. When making modifications to a computer, keep this in mind.

NOTE: Not all manufacturers observe this convention.

Six cables

So, the seven basic connectors are:
2)Monitor power
4)Serial port
5)Parallel Port
6)Game port
7)Monitor port.

Once the cover is removed we can see the guts of the computer. Lay the computer flat with the drives facing you. In the top, right-hand corner we see a silver cube. From the connectors attached we can identify this block as the power supply. Its colored cables attach to the motherboard and disk drives. All of these are inside the computer case.


Expansion cards fit in slots on the motherboard and the spoon (the metal plate) is screwed to the back of the case. On normal motherboards, these expansion cards mount vertically. On some computers they mount to a riser card. The riser card is mounted to the motherboard and the expansion cards sit parallel to the motherboard.

In the front of the case we see the disk drives. Hard drives are most often hidden behind cover blanks. Unlike floppy and CD-ROM disks that are inserted and removed, hard disk media is sealed inside so no front panel access is needed. Drive access is indicated by a HDD (hard disk drive) access LED on the front panel.

The parts outside the computer are called peripherals.

Finally, there is the motherboard. It contains the heart and soul of the computer. The motherboard is the large board that the expansion boards attach to.

That describes the major parts of an IBM PC compatible clone. For information on the major sub-components, click on the colored links.

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Updated March 4, 2004 at 10:07 pm.