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FREE online courses on the Basics of a Computer - Characteristics of Computers




The computer was invented as a high-speed calculator. This has led to many scientific projects which were previously impossible. The control of the moon landing would not have been feasible without computers, and neither would today's more scientific approach to weather prediction. If we want tomorrow's forecast today (and not in six months time) meteorologists can use the computer to perform quickly the necessary calculations and analyses. When making flight reservations we want to know well in advance of take-off that a seat will be available - if it is not, then we have time to make other arrangements. The ability to get answers fast enough so that one has time to take action on them (or to make alternative plans, as in the case of airline reservations) makes real-time computing possible.


Electrical pulses travel at incredible speeds and, because  the computer is electronic, its internal speed is virtually instantaneous. We do not talk in terms of seconds or even milliseconds. Our units of speed are the microsecond (millionths), the nanosecond (thousand0millionths) and latterly even the picosecond (million-millionths). A powerful computer is capable of adding together two 18-digit number in 300 to 400 nanoseconds.


Consider two examples from non-numerical environments. The manual indexing of the complete works of Thomas Aquinas (approximately 13 million words) would have taken 50 scholars about 40 years to accomplish. With the aid of a computer a few scholars did it in less than one year. Fingerprint identification, in time to catch a criminal before he flees the country, would be impossible without computers. The first example enables us to enjoy knowledge that would otherwise be unobtainable within our own lifetime. In the second example, the police gain time in which to act.




The speed with which computers can process large quantities of information has led to the generation of new information on a vast scale, in other words, the computer has compounded the information 'explosion'. How can people cope with it? We can't, but computers can. But where do they keep it all?


As a human acquires new knowledge, the brain subconsciously selects what it feels to be important and worth retaining in its memory, and relegates unimportant details to the back of the mind or just forgets them. In computers, the internal memory of the CPU is only large enough to retain a certain amount of information. It is therefore, impossible to store inside the computer the records, for example, of every Premium Bond and the names and address of their owners. All of this data is stored outside of the memory of the CPU, on auxiliary or secondary storage devices. Small sections of the total data can be accessed very quickly by the CPU and brought into the main, internal memory, as and when required for processing.


The internal memory (in CPU) is built up in 1 K or K modules, where K equals 1024 storage locations. Babbage's Analytical Engine would have been capable of holding 1000 numbers, each of 50 digits. Computers come in many sizes. Many small micro-computers have an 8 K or 16 K store whilst 'super computers', such as the CDS CYBER 205 may have up to 1024 K stores (i.e. 1024 * 1024 locations).




In spite of misleading newspaper headlines, the computer's accuracy is consistently high. Errors in the machinery can occur but, due to increased efficiency in error-detecting techniques, these seldom lead to false results. Almost without exception, the errors in computing are due to human rather than to technological weaknesses, i.e. to imprecise thinking by the programr, or to inaccurate data, or to poorly designed systems.




Computers seem capable of performing almost any task, provided that the task can be reduced to series of logical steps. For example, a task such as preparing a payroll or controlling the flow of traffic can be broken down into a logical sequence of operations, whereas comparing the tones of a turner with a Vermeer cannot. Yet the computer itself has only limited ability and, in the final analysis, actually performs only four basic operations:


It exchanges information with the outside world via I/O devices,

It transfers data internally within the CUP,

It performs the basic arithmetical operations,

It performs operations of comparison.


In one sense, then, the computer is not versatile because it is limited to four basic functions. Yet, because so many daily activities can be reduced to an interplay between these functions, it appears that computers are highly ingenious. Programming is the craft or reducing a given problem into an interplay between these few operations.




A computer is much more than an adding machine, calculator or check-out till, all of which require human operators to press the necessary keys for the operations to be performed. Once a program is in the computer's memory, the individual instructions are then transferred, one after the other, to the control unit for execution. The CPU follows these instructions until it meets a last instruction which says 'stop program execution'. When Babbage claimed that his Analytical Engine would be automatic, he meant that once the process had begun, it would continue without the need for human intervention until completion.




Being a machine, a computer does not suffer from the human traits of tiredness and lack of concentration. If 3 million calculations have to be performed, it will perform the 3 millionth with exactly the same accuracy and speed as the first. This factory may cause those whose jobs are highly repetitive to regard the computer as a threat. But to those who rely on a continuous standard of output, e.g., quality control in the refining of oil and other chemical processes, the computer will be seen as a considerable help.

The Basic Anatomy of the Computer


Remembering Babbage's Analytical Engine, let us see what happens in a computer. It receives information (input); it processes this information in some way according to set of precise instructions (in the CPU); and it then presents the results in a useful form (output).


On closer inspection we find that the CPU (the computer itself, remember) has to store the information in a memory before it can carry out processing operations. Two kinds of information have to be input, the program and the data. The program is the set of instructions which the computer is to carry out, and the data is the information on which these instructions are to operate. For example, if the task is to sort a list of telephone subscribers into alphabetical orders, the sequence of instructions or procedure which guides the computer through this operation is the program, whilst the list of names to be sorted is the data.


In the Analytical Engine calculations were to be handled by an arithmetic unit which Babbage called the Mill. The computer also has an arithmetic unit. Arithmetic, because all computer operations involve the manipulation of numbers. All information, program and data, are represented in numeric form. The manipulations also include making comparisons and logic type operations as well as arithmetic operations ( + - * / ), and for this reason the unit is referred to in full as the arithmetic and Logic Unit (ALU).


The Electronic Discrete Variable Automatic Computer (EDVAC) in 1952, was to be one such computer. The memory unit stored both the instructions and data to be used for the calculations.


In 1946, Ekert and Mauchly formed their own company, which in 1949 was incorporated as the UNIVAC division of the Remington Rand Company Ltd., In 1951 the UNIVAC I, i.e. the computer developed by Ekert and Mauchly became operational at the Census Bureau. This computer was self checking and used magnetic tape for data input and output. The UNIVAC I was run 24 hours a day until 1963. Yet, another UNIVAC I was put to business by the General Electric Corporation in 1954.


The first generation of computers was marked by the use of vacuum tubes as the electronic components and by the use of either electrostatic tubes or mercury delay lines for storage. Power tapes and punched cards were also used. Electronic time per operation ranged from 0.1 millisecond, while memory access time was 1 millisecond.



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