OPTICAL SCANNER.\ An optical scanner can be used to scan (read) graphic art or text directly into the microcomputer. This saves redrawing or retyping.

CD-ROM DRIVE.\ You may have a CD-ROM (compact disk-read only memory) drive to read data stored on compact disks. CD-ROM technology is the same as that used for audio disks, except it includes routines for detection and correction of data errors. The CD-ROM drive can be internal or external to the system unit. Compact disks can hold a vast amount of information, 550MB or more. They are used when the same information is needed by many, and the information is fairly constant. For example, libraries can put all the information they need about documents and publications on a CD-ROM. On a CD-ROM, the information, once recorded, cannot be erased or changed, but it can be read many times. The expression Write Once, Read Many (WORM) describes this type of technology.

SWITCH BOXES.\ When you want to share printers, you can connect them through a switch or switch box. For example, two or more computers can use one printer, or one computer can use two or more printers. As you can see, you will need a cable between the switch box and each device. You then switch the setting, A or B, on the box to switch signal lines without disconnecting and reconnecting cables. Switches range from this simple, manually operated switch box with two settings to switches that select signal lines automatically and provide buffering capability. Some also provide for both parallel and serial devices.

MODEMS.\ Modems provide communication between systems. Through them, your system can send or receive data over phone lines. You may also use a null modem cable for communication between systems that are close enough to each other to be connected by cable. A null modem cable creates a communications link that allows devices to communicate without using modems and phone lines. To make the systems and null modem cable fit together, you may need a gender connector or gender changer to bridge two like connectors.

As you can see, a basic (low-end) system is only a _beginning. As you become more familiar with microcomputers and as technology changes, you will find more and more capabilities and more uses for microcomputers.