How it works : Computers
|Ever since man began to count and do simple arithmetic he has tried to
make the process easier and faster by the use of machines. From counting
on his fingers, man progressed to using pebbles to represent numbers, and
this led to the invention of the ABACUS (a form
of digital computer), a device that is still widely used in many countries
A major advance in mathematics was the system of calculation by LOGARITHMS, devised by John Napier at the end of the 16th century and first published in 1614. Following this discovery, the English clergyman William Oughtred invented sliding scales, an early type of SLIDE RULE which, by its use of lengths to represent numbers, is in effect a form of analog computer. The abacus, which operates by counting rather than measuring, is in comparison a digital device.
The first mechanical CALCULATING MACHINES appeared during the 17th century. Blaise PASCAL produced a machine that could add and subtract, performing multiplication and division by repeated addition and subtraction. Some years later Leibniz invented a calculator which could perform all these functions individually.
The true ancestor of the modern computer was designed by Charles BABBAGE in the 1830s. This machine, the Analytical Engine, was never completed, but it was intended to perform any desired calculation automatically by means of a mechanical calculating unit controlled by punched cards. These punched cards, originally developed for the JACQUARD LOOM, formed the basis of the CARD HANDLING MACHINES developed by Dr Herman Hollerith in the 1880s.
Two years later, at the University of Pennsylvania, Dr John Mauchly and J Presper Eckert completed the first electronic digital computer, the Electronic Numerical Integrator and Calculator (ENIAC). it contained over 15,000 VALVES [vacuum tubes] which produced a great deal of heat and developed frequent faults, but it could perform as much work in one hour as ASCC could in a week. Although instructions were stored internally, it took hours of manual rewiring to change programs.
At the beginning of the 1950s many commercial organizations were working on the development of computers. The first of these machines to appear on the market were the Leo, made in Britain by a subsidiary of J Lyons, the catering company, and the UNIVAC I (Universal Automatic Computer), built in America by Eckert and Mauchly for Remington Rand and delivered to the US Census Bureau in 1952.
As transistors became more reliable and widely available during the 1950S the computer makers began to incorporate them into their designs, using transistorized circuits in many parts of the machines in conjunction with the valve [tube] circuits. In 1960 the Control Data Corporation marketed the first fully transistorized computer, and in the following years INTEGRATED CIRCUITS became an important feature of computer design. Improvements in computer peripherals, the input, output and storage devices such as card, tape and disk machines, have also been significant during the last twenty years.
They are also used in industrial process control, and in navigation equipment such as that in SPACE VEHICLES: in these cases the output signals can be used to control the operation of other mechanisms.
The first generation of machines, beginning with ASCC and ENIAC, were those based on valve [tube] circuits. The development of the transistor and other semiconducting devices led to the second generation of computers which used these in place of the valves; about 1965 the introduction of miniaturized integrated circuits to replace the transistors resulted in the third generation computers. With each advance in systems technology computers have become smaller and more powerful, a factor which has led to great increases in the ratios of cost to performance and which brings the prospect of computers in the home much nearer to reality.[As we all know - this HAS become a reality - JOS]
For reasons of size and cost it is not possible to store files of data permanently in the main storage (the MEMORY) of the system, and so a backing store, usually in the form of magnetic tape, magnetic disks or magnetic drums, is used for DATA STORAGE. These devices also act as input and output units, transferring data to and from the central processing unit (cpu).
The control unit reads the program instructions, and issues commands to the other parts of the system in order to carry out these instructions.
The arithmetic and logic unit performs computations as instructed by the control unit, adding, subtracting, multiplying, dividing and for comparing values. During calculation, numbers are stored in areas of the arithmetic and logic unit called registers. Information can be moved from one register to another. A simple ADD instruction will, for example, take a number from its register and add it to another in the accumulator) a type of register where the addition takes place. The result of the addition may be put into the memory to await further computation, passed to an output device such as a printer or display screen, or recorded in the backing store.
The paper tape and punched card machines are relatively slow devices compared with the magnetic units, which are fast access storage devices that the control unit can call on at any time, extracting data from them and recording more onto them. Most modern tape and disk units can simultaneously 'read' and 'write' (record) data, which greatly increases their effective speed, and the latest disk units can transfer data at a rate of up to 2 million characters per second.
The transfer of information from source documents to the input media (data preparation) has to be done manually, which makes it slow and costly. Most computers can produce a printed output, but the acceptance of printed input presents a problem, as different sizes and types of print, unusual characters and unnecessary information make the direct input of non-standardized documents impractical. For this reason systems using optical CHARACTER RECOGNITION require the data to be typed or printed on standardized forms using a specially-designed typeface such as E13B or OCR-B, which is styled to avoid possible confusion between similar characters such as zero and capital 0.
Line printers, so called because they print a complete line at a time, work at speeds up to 2000 lines per minute. The paper is in the form of a continuous perforated sheet with interleaved carbon paper, and after printing the sheets may be separated in a decollator. Output can also be generated in the form of graphs or diagrams by automatic plotters.
Such a system often involves time sharing, where the cpu handles more than one task at a time, splitting each one into a series of operations and then dealing with all these operations in a predetermined sequence until the tasks are completed. It may also use multiprogramming, loading the machine with several programs that are run concurrently so that the system can handle more than one rype of problem at a time. These operations are carried our in real time, that is, computation of the input data, revision of the data files, and display of the result follow almost immediately from the original enquiry, so if for example a customer has withdrawn some money from his account, the details of the transaction will be recorded, the new balance computed and displayed, and the account records updated, all in a matter of seconds. Other computing operations such as payroll calculations, where the data is accumulated over a period of time before processing, are called batch processing.
COBOL (COmmon Business Oriented Language) was developed as a more alphabetically based business language, so that instructions written in this language came nearer to ordinary language. It has therefore come to be one of the most widely used commercial programming languages, enabling people who are not trained programmers to participate in the writing of programs. A typical COBOL statement may simply be 'SUBTRACT TAX FROM GROSS GIVING NET'. Computer languages are often referred to as being 'high level' (near to man) or 'low level' (near to machine).
The basic software of a system comprises the machine language programs, compilers and assemblers to translate high level languages to machine code, and a program library of commonly used basic programs (routines and subroutines) that are frequently employed by a particular user. The main applications programs are written to instruct the machine to perform the specific data processing functions required by its user. All of these programs, with the principal exception of the main supervisori program, are usually kept in the backing store. The main supervisory program is loaded permanently into the main store, and it controls the other programs, bringing them temporarily from the backing store into the main store when rhey are needed.
A suite or group of computer programs combine to perform one specific job, for instance a payroll. A software system is a combination of various suites of programs to perform a broader task. For example, it will take several programs to evolve a production control system for a factory, include reports on stock movement, work in progress, purchasing, production line workloads and availability of raw materials. A systems analyst will examine the total problem, divide it into sub-groups and assign programmers to each sub-group to write the software.
When digital machines are used for controlling production processes they are often dealing with continually changing quantities, temperatures and pressures for example, and this analog data is converted into digital for the machine to process it. On the basis of the data it receives the computer makes decisions, which are then converted back into analog form to control the machinery, pumps and actuator of the manufacturing plant.
The hardware used in mixed analog and digital computing usually consists of separate analog and digital computers, which are connected together via a hybrid interface. This interface is a piece of equipment which converts the analog data to digital form and vice versa.
Increasingly, however, small organizations are setting up their own small systems based on 'mini-computers'. These systems have all the main features of a large computer, but have a lower performance in terms of speed of operation or quantity of data that they can handle. Many of these small systems are, however, quite powerful, and in some cases will support a number of local or remote terminals.
Reducing hardware costs make it likely that more and more companies will opt for small systems, with larger organizations supplementing their existing systems with mini-computers, or even replacing large systems with a number of interconnected small systems.
A number of input/output (I/O) devices are used with these small systems, including printers, paper and magnetic tape units, and data collection units that record alphanumeric data-both letters and numbers-onto magnetic tape CASSETTES or small flexible magnetic disks ('floppy disks'). Many of these small systems are as powerful as some of the older full-size machines, but are much easier to use.
Reproduced from HOW IT WORKS p629