When data is transmitted directly to the computer over long distances, it is necessary to add two other devices, one at each end. These devices are called modems. The word modem is an acronym for MOdulator-DEModulator. A modem converts the digital signal produced by a computer to asuitable audio signal for transmission over communication lines (I/0

Fisnnre 3-2.-Serial and parallel data transmission.

channels). The modem at the other end of the line reconverts the audio signal back to a digital signal before sending it to the CPU. If this conversion (digital to audio) was not carried out, the digital signal would degenerate during transmission and become garbled. Modems are commonly used to send and receive data over telephone lines, making them a very valuable tool for imaging facilities.

COMPUTER SYSTEM SOFTWARE Software plays an important role in computer operations. Without software, a computer could not perform simple addition. It is the software that makes everything happen. "Software" may be defined as all the stored programs and routines (operating aids) required to use the capabilities of a computer system fully. Basically, two types of software are used: systems software and applications software.

 SYSTEMS SOFTWARE

Systems software is often referred to as systems programs. Systems software consists of supervisory and support programs designed to coordinate the capabilities of the computer itself. These include programs, such as operating systems, assemblers and compilers, and utilities.

Operating Systems

An operating system is a collection of many programs used by the computer to manage resources and operations. These programs control the execution of other programs. They schedule, assign resources, monitor, and control the work of the computer. These actions are carried out without human intervention. Assemblers and Compilers

Both assemblers and compilers are language translators. They are designed for specific machines and specific languages. They translate computer programs written in programming language into machine language. A language translator for an assembly language is called an assembler program. Most high-level language translators are compiler programs. These translators are designed to convert artificial languages used by programmers into machine-usable code after it is entered into the computer.

Utility Programs

Utility programs perform tasks, such as sorting, merging, and transferring data, from one I/0 device to another. They may be separate programs, or they may be included in an operating system to help the user perform these tasks. Text editors may also be included in an operating system so the user can enter, add, delete, or change program statements; debug routines may also be included to help the user locate errors.

APPLICATIONS SOFTWARE

Applications are those particular programs designed to solve individual user problems. These programs can be written by you, the user of a computer system, developed by a central design agency, or they can be purchased from a software firm. Numerous types of applications programs are written. They range from games to word processing and electronic imaging.