Topic 6. Personal computers

Personal computers are supposed to appear in the late 1970s. One of the first and most popular personal computers was the Apple II, introduced in 1977 by Apple Computer. During the late 1970s and early 1980s, new models and competitive oper­ating systems seemed to appear daily.

The first generation of true personal computers, which came -on the market between 1977 and 198.1, had eight-bit micropro­cessors; later introduced systems had 16-bits ones. Now 32-bit microprocessor chips are available, and soon they will be includ­ed in complete computer systems. " ~"

What is a personal computer? How can this device be char­acterized?

— First, a personal computer being microprocessor-based, its central processing unit, called a microprocessor unit

— Second, a PC has a memory and word size that are smaller than those of minicomputers and large computers.

— Third, a personal computer uses smaller, less expensive, and less powerful input, output and storage components than do large computer systems.

— A PC employs floppy disks as the principal online and offline storage devices and also as input and output media.

— Finally, a PC is a general-purpose, stand-alone system that can begin to work when plugged in and be moved from place to place.

Probably the most distinguishing feature of a personal com­puter is that it is used by an individual, usually in an interactive mode.

Types of computers

The two basic types of computers are analog and digital.

Analog computers simulate physical systems. They operate on the basis of an analogy to the process that is being studied.

Digital computers, as contrasted with analog computers, deal with discrete rather than continuous quantities. They count rather than measure. They use numbers instead of analogous physical quantities to simulate on-going, or real-time processes.

Topic 7.COMPUTER PROGRAMMING

Programming is the process of preparing a set of coded in­structions which enables the computer to solve specific prob­lems or to perform specific functions. The essence of computer programming is the encoding of the program for the computer by means of algorithms.

The phase in which the system's computer programs are written is called the development phase. The programs are lists of instructions that will be followed by the control unit of the central processing unit (CPU). The instructions of the program must be complete and in the appropriate sequence. To guard against these errors in logic and to document the program's logical approach, logic plans should be developed.

There are two common techniques for planning the logic of a program.

The first technique is flowcharting. A flowchart is a plan in the form of a graphic or pictorial representation that uses predefined symbols to illustrate the program logic. It is, there­fore, a "picture" of the logical steps to be performed by the computer. Each of the predefined symbol shapes stands for a general operation. The symbol shape communicates the nature of the general operation.

The second technique for planning program logic is called pseudocode. Pseudocode is an imitation of actual program in­structions. It allows a program-like structure without the bur­den of programming rules to follow. Pseudocode is less time-consuming for the professional programmer than is flowcharting.