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.
