Foot Print - One of the Buzz words you will hear about a computer case is the "footprint." This term refers to the actual space required to set a computer on your desk.

It also refers to the size of the internal components. Smaller case styles tend to be more difficult and time consuming to repair or upgrade.

Proprietary Components - Some manufactures also tend to use their own external connectors that are available only from the seller.

This tends to drive the cost of upgrades or replacement of defective components upwards.

It is really no different than what car manufacturers do each model year. You might be able to tell something from the outside of a car, but the computer case really gives you no indication on how well the computer works. (what's under the hood?) The two basic type are:

Desk Top Case (Full) - This machine is made to rest in a flat position on a desk or table top. This is the classic or original style of the Pc. There are four basic versions of this type case. The difference in these cases are mainly the size, position of the on/off switch and the number of floppy drives they can hold.

• PC Style Case - This case is 21" wide by 17" deep by 5.5" high with room for 2 full height floppy drives and 5 expansion slots.

• XT Style Case - Same as above but with 8 expansion slots.

• AT Style Case - This case is 23 " wide by 17" deep by 6.6" high with room for three half height floppy drive units.

• Baby AT style Case - The dimensions vary from manufacturer to manufacturer. The typical case size might be 16" wide by 15" deep by 5" high

• The Full Tower - The tower case has much more room then the mini-tower or conventional desk top case. There is usually room for seven or eight internal drives and it is designed to set on the floor next to your desk. The average height of the tower case is about 21 inches high.

• The mini- or Half Height Tower The mini-tower is smaller and has less room for drives. Measuring about 16" high, this case is designed to sit on your desk.

Depending on the design of the computer you will see different combinations of features and indicators. Some of the more common features you will see Include:

• Power Indicator - Every computer will have one of these. It is a small Light Emitting Diode (LED) that illuminates when the power switch is turned on. The most common symbol for this indicator is the light bulb located next to the light.

• Disk Access Light - The disk access light is a Light Emitting Diode (LED) that is connected to your hard drive. The light will appear to flash as your computer goes to the Hard disk to get data. In this way you can tell if the system is actually using the hard drive. The common symbol is a can or drum located near the LED.

• Turbo Speed Indicator - Many of the older computers had a feature called the "Turbo Option". This title is misleading as in some computers the use of this switch actually slows down the computer. The purpose of this switch was to actually slow down the speed the CPU is operating at. Many of the older programs were written in such a way as to work well with slower CPUs. As an example some of the computer games like Pinball or Tennis are written with a specific speed in mind. If the computer speed is not slowed down when playing these older games, you would not be able to keep up with the ball.

• The Reset Button- Turning the power off and then on again is called a "Cold Boot." When this is accomplished, everything in your computer is reset to its original condition. Some manufacturers provide a reset switch that will re initialize the system without sending the normal power surge associated with turning on the power switch.

• On/Off Switch - The on/off switch does more than turn the computer on and off. It also acts as a circuit breaker just like the ones in your house. This switch provides protection from high voltage and current. Not all computer cases have the on/off switch on the back. Some are found on the side of the case. Tower systems have the switch on the front of the case.

• Power Input - The power supply plugs into standard house wall outlets (115 Va). Many people use power strips that provide additional surge protection and allow you to plug all your components into one source with a single switch.

• 110-220 Switch (115/230) - As you may know, standard house current is not the same world-wide. In the US we use 110-115 volt, 60 cycle current. In Europe they use 220 volt, 50 cycle current. Most computer power supplies can handle both types but you must set the switch on the power supply to the correct voltage.

• Ports- A port is a connection where the computer can be attached to an external device.

  For instance, there may be ports for your printer, MODEM keyboard and monitor. You will notice a series of covered vertical slots on the back of your computer. These slots provide access to expansion cards or ports attached to the motherboard inside the computer. Each of these cards or ports will have a specific type connector.

  • Keyboard Port- All computers have a keyboard port. There are two types of keyboard connectors currently in use. The older PC, XT, and AT style computer used a large 5 pin DIN plug. Most of the modern computers are using the much smaller IBM PS2 style connector..

  • Bus Mouse - The older PC, XT, and AT style computer used serial port connections for mice. The majority of newer system now have what is called a "Bus Mouse." These mice use a mini 6 pin DIN and connect directly to the bus on the motherboard.

  • Video Port - The video port is the connection between the video controller and the monitor. There are two basic connectors. A nine pin connector for black and white, CGA, and EGA screens and a 15 pin for VGA screens.

  • Serial Ports - Serial ports are standard input/output connections. They use either a 25 pin or 9 pin male connector. Devices such as a serial mouse can be connected to these ports.

  • Parallel Ports - Almost every personal computer made today will have at least one parallel port. These ports are used to connect your printer. The connector on the computer will always be a 25 pin female connector.