Modems
External disk drives
Your computer is designed to communicate with peripherals by way of the connectors on the rear panel of the main system unit. The connectors are called “ports,” and allow information to be sent back and forth between the system CPU and a peripheral device.
Your keyboard and your video monitor connect to the main system unit by way of two specialized ports. The keyboard is connected to the “Keyboard port” on the rear panel of the main system unit. If you have purchased a video monitor system for your computer, the display monitor is connected to the “video port” on the rear panel of the video controller card, which is mounted inside your main system unit.
Since your system CPU must be in constant communication with both the keyboard and the display monitor, specific circuits connect them together. Since other peripheral devices only communicate with the system CPU occasionally, they can use general purpose ports.
Computerized data is composed of electronic words called “bytes.” As an example, each letter or number that appears on your display monitor has been sent from the main system unit to the monitor itself in the form of a single byte. This byte is made up of individual “bits.” in the same way that a word is made up of letters. In order to keep things consistent for the system CPU, bytes are made up of groups of eight bits. Using