What is a Computer?
It’s very easy to use the term computer glibly without bothering to say what it actually means. Part of the reason for this situation is that today’s computer is virtually synonymous with the PC. This box briefly looks at some of the ways in which we use the term computer.
1, The human calculator The computer historian David Alan Grier wrote a book called When Computers Were Human that describes a period of history when people performed scientific calculations by hand. In the Victorian era, some people were professional computers and spent their working lives doing arithmetic with a pencil and paper.
2. The mechanical computer In order to increase the productivity of human computers, mechanical devices were invented to mechanise the operations of addition, subtraction and multiplication. Later, these basic mechanical devices were extended to perform the more complicated calculations involving polynomials.
3. The Analog Computer Largely forgotten today, the analog computer used electronic circuits to synthesise physical systems. For example, an analog computer can imitate the behaviour of a car’s suspension system by putting together components that mimic the behaviour of springs and dampers in a car’s suspension system. You don’t program an analog computer in the normal sense of the word program. You construct an electronic equivalent and then observe its behaviour. You do not have to write a program.
4. The electro-
5. First generation electronic computers The first electronic computers used vacuum
tubes rather than electro-
6. The von Neumann machine The so-
7. The dedicated computer The dedicated computer is designed to solve a single problem
or set of problems; for example, the computer in an automobile’s anti-
8. The general-
9. The mainframe Once, the mainframe computer was an immensely expensive general-
10. The microprocessor The microprocessor is a computer on a chip. It can be part
of a general-
11. Embedded computer The embedded computer is a specific form of the dedicated computer
that is intended to control part of a much larger system. Embedded systems often
12. Reconfigurable computer A significant change in computer technology occurred
in the 1980s with the introduction of complex programmable logic elements; that is,
the interconnection between logic elements on a chip could be performed by programming.
Today we have logic systems that can be programmed and reprogrammed, and complex
circuits can be modified under software control. Now, we can not only change a program,
but we can also change the hardware on which it runs. This has important implications
for the small-
12. Quantum computer Today’s digital computers use semiconductor technology based
on silicon. Quantum computers make use of the quantum states of individual atoms
to store information and perform computation. In theory, quantum computers are immensely
more powerful than semiconductor-
13. Biological computer The complex organic molecules of DNA can carry encoded information in the form of nucleotides. By performing chemical operations on these molecules, computation becomes possible. It has also been demonstrated that logic gates can be synthesized from individual cells. Although very simple functions have been created, biological computing is still only a dream.
14. Neural computers A neural computer, or, more commonly, neural network is modelled on the behaviour of the neural cells of the brain. A neuron has several inputs and an output. The neuron fires if the weighted sum of the inputs exceeds a certain threshold. The weighted sum means that the value of each input is multiplied by a constant and all products summed (the multiplier constant is different for each input). A neural computer is created using interconnected artificial neurons. Unlike quantum and biological computers, neural networks are already a practical technology. Moreover, they can be programmed by learning (matching inputs with outputs). Neural nets are not intended to create conventional computers but to solve specific problems that are related to pattern matching; for example, reading handwriting, or predicting the movement of the stock exchange). The neural network is more related to the analog computer than the von Neumann machine.
15. Fuzzy logic In the 1970s fuzzy logic was introduced to model systems that were either difficult to quantify or uneconomic to solve using conventional computers. Fuzzy logic allows you to build a control system (for example; an automatic breaking mechanism on an underground rail carriage) with an incomplete modelling of the system. Inputs are quantized into regions or zones and then fuzzy logic operators are applied to them. For example, IF speed less than 5 AND acceleration less than 4 and distance to go greater than 10 THEN apply level 6 braking.