Text 13(c) Digital computers

Computer equipment may be divided into two major classifications: analog and digital.

A digital device operates directly upon numbers. Its basic operation is counting, whether the counting of beads, of gear teeth, or of electrical pulses. All of the mathematical operations are performed by counting or addition. In digital computation a problem is broken down into a series of arithmetic steps which are completed in sequence to arrive at the solution. This method is known as a sequential operation and is in effect the same as if a pencil and paper were used to carry out arithmetic operations. The difference, of course, is that the tremendous speed and memory capacity of the digital computer permit complex calculations to be made in a fraction of a second. A point to emphasize is that mathematical operations and the method by which the computer derives a final result have little, if any, resemblance to the actions of the physical problem under study.

The accuracy of digital computer solutions is theoretically unlimited. The precision of a digital computer is readily increased by providing additional decimal places in the numbers throughout the equipment. However this both increases the cost of the equipment and decreases the speed of computation.

Because of its numerical nature, the digital computer is well suited to problems involving the processing of large masses of data where single calculations are repeated over and over again. Consequently, digital machines find their widest use in scientific problems involving statistical analysis and in business applications such as accounting and record keeping.

Digital computers are also being applied to the control of industrial processes. The computer generally performs supervisory function by evaluating process conditions against desired performance criteria and determining changes to provide optimum operation. More recently, digital computers have been used to provide direct digital control (DDC) of individual process variables.

Unit 14

Grammar:

Complex Subject

Text 14(a) Superconductivity

The low temperature physics deals with various phenomena occurring at temperatures in the region of absolute zero (- 273 ºC). The lowest temperature on Earth is known to have been registered in the Antarctic – about – 80 ºC. Still lower temperatures are claimed to be found on other planets. On Saturn, for instance, it reaches –153, on Uranus –173, on Neptune –193. On Pluto – the planet most remote from the sun- the temperatures appear to be below –218 C. Even this, however, is believed not to be the limit. A temperature of – 273 ºC has been found to be possible in nature. In laboratory experiments scientists have achieved a temperature, which differs from absolute zero by 1/10,000 of a degree.

Having learnt to control heat, man has multiplied its potential many times over, learned to cut and melt metal and found many other useful applications for it. Cold is considered to be quite useful.

The study of different substances at low temperatures has revealed many interesting phenomena. One of the most amazing (surprising) was superconductivity –the complete loss of resistance to electrical current. This property has been found in more than 20 metals. If an electric current is sent through a ring of cooled metal of this type, it will circulate for a very long time.

Superconductivity has long been the subject of pure theory and it seemed that it would never be possible to apply it in practice. However, instruments have been developed using this phenomenon.

Of particular interest are the superconductive alloys widely applied in the development of superconductive magnets, which make possible, with a small expenditure of power, to obtain permanent magnetic fields of scores and hundreds of thousands of oersteds .

Of great interest are recent theoretical studies that indicate the possibility of developing superconductors retaining their properties at room and even higher temperatures. Their practical application could open up a new chapter in the use of electric power. It could multiply the efficiency of electrical machines and save billions of kilowatt hours in transmitting power over long distances.

NOTES

1.oersted – ерстед, одиниця магнітного опору