TEXT A. CENTRAL PROCESSING UNIT

1. The central processing unit (CPU) or central processor is the nerve centre of any digital computer system, since it coordinates and controls the activities of all the other units and performs all the arithmetic and logic processes to be applied to data. All program instructions to be executed must be held within the CPU, and all the data to be processed must be loaded first into this unit. It is convenient to consider the central processor to have three separate hardware sections: an internal or main memory, an arithmetic and logic unit, and a control unit. The role of the internal memory was discussed more detailed in the previous lesson.

Now let us discuss the latter two sections.

2. The CPU has two functions: it must (1) obtain instructions from the memory and interpret them, as well as (2) perform the actual operations. The first function is executed by the control unit. This unit in its turn must perform two functions: it must interpret the instruction; then, on the basis of this interpretation (2) tell the arithmetic and logic unit what to do next. The latter function is accomplished through the use of electronic signals. According to these two functions we can separate the part of the control unit that interprets or decodes the instruction called the instruction decoder from the part that generates the control signals called the control generator.

3. An instruction having been transmitted to the instruction decoder, where it is interpreted, the control generator senses this interpretation and then produces signals that tell the arithmetic unit which operation to perform. It also generates signals that choose the proper numbers from the memory and sends them to the arithmetic and logic unit at the proper time; and when operation has been performed, other control signals take the result from the arithmetic and logic unit back to the internal memory. After an instruction has been executed, the control generator produces signals that cause the next instruction to go from the memory to the instruction decoder.
In this way the instructions arc performed sequentially.

4. The second function of the CPU is performed by the arithmetic and logic unit which does the actual operations. This unit is capable of performing automatically addition, subtraction, multiplication, division, comparing, selecting, and other mathematical and logical operations. Consider now what happens in the arithmetic and logic unit while an instruction is being executed. In most computers only one word at a time can be transferred between the arithmetic/logic unit and the memory. Hence, to perform an operation involving two arguments, the first argument must be transferred from the memory to the arithmetic/logic unit and stored there temporarily while the second argument is being transferred. The special memory cell in the arithmetic/logic unit /or this purpose is called the accumulator. The operation being performed, the result is formed in the accumulator before it is transmitted back to memory.

5. Next consider the instruction decoder that interprets instruction. In order that the instruction decoder perform its function, it must constantly refer to the instruction being interpreted during the time control signals are being set up. To facilitate this, while an instruction being executed it is stored in a special memory cell called the instruction register, located in the instruction decoder.

6. There is another memory cell located in the instruction decoder called the current-address register. The contents of this register is always the memory address from which the instruction being executed came. The reason for this is related to the fact that the address of the present instruction was given as part of the previous instruction.

For the computer designer to understand the work of the CPU is quite necessary.

Notes

1. during the time control signals are being set up - во время формирования сигналов управления

2. The reason for this is related to the fact - Причина этого заключена в том

Exercises

IV. Find in (b) the Russian equivalents to the English words and combinations in (a):

a) hence; for example; according to; by means of; i.e.; etc.; always; just; on the other hand; since; any; in its turn; sometimes; the same; while; in this way; instead (of); usually

b) то есть, например; всегда; только что; с другой стороны; так как; в свою очередь; иногда; тот же самый; любой; следовательно; и так далее; в то время как; таким образом; вместо; согласно; обычно; посредством

V. Arrange synonyms in pairs:

semiconductor technology; to execute; to write; to control; memory to sense to choose; to form; to feel; storage; to store; to set up; to handle; solid-state technology; to perform; to keep; to select; research; to put in; investigation

VI. Complete the following sentences:

1. The arithmetic/logic unit is capable of ... . 2. The access time is the time required for transmitting one computer ... out of the ... to where it ... . 3. The actual- computations are executed in a central ... . 4. The part of the control that interprets the instruction is called ... . 5. The part of the control that generates the control signals is called ... . 6. The control signals choose the proper numbers from and send them to ... at the proper time.

VII. Memorize the following definitions:

1. The CPU is the nerve centre of any computer since it coordinates and controls the activities of all the other units. 2. The arithmetic/logic unit is that part of the CPU in which the actual computations take place. 3. The control unit is that part of the CPU which obtains instructions from the memory, interprets them and generates the control signals. 4. The instruction decoder is the part of the control unit which interprets or decodes the instruction. 5. The control generator is the part of the control unit which generates the control signals. 6. The instruction register is the part of the instruction decoder in which the address of current instruction is stored. 7. The current-address register is the second special memory cell located in the instruction decoder. 8. The accumulator is the special memory cell in the arithmetic/logic unit in which the result is formed before it is transferred back to the memory unit.

VIII. Answer the following questions:

1. What is the general purpose and function of the CPU? 2. How many parts is the CPU composed of? 3. What is the general purpose of the control? 4. What is the arithmetic/logic unit? 5. What is the instruction decoder? 6. What is the general function of the control generator? 7. What happens in the CPU while an instruction is being executed? 8. What is the accumulator? 9. Where is the accumulator located? 10. Where are the instruction register and the current address register located? IX. What do you call a unit which:

1) interprets instructions? 2) senses the interpretation of instructions and produces control signals? 3) performs mathematical and logical operations? 4) chooses the proper numbers from the internal memory and sends them to the arithmetic/logic unit at the proper time? 5) obtains instructions from the main memory, interprets them and accomplishes the actual operations?

IX. Compare:

a) a memory and a CPU; b) an accumulator and an instruction decoder; c) an arithmetic/logic unit and a control unit

X. Read and translate the following sentences paying attention to the objective infinitive constructions and for-phrases with the Infinitive:

1. Our engineers want the complex problems to be solved by computers. In the laboratory we saw the perforator punch holes in the cards of standard size. 3. It is quite necessary for the programmer to understand the work of all units of a computer. 4. We watched the floppy disk begin to operate. 5. The speed of the computer may be found by measuring the time which is required for it to transmit one word out of the memory to where it will be used. 6. We asked the lab assistant to show us the computer operate. 7. There is a good reason for us to use this kind of the bubble memory in a personal computer. 8. Information has to be in the form of digits or characters for a digital computer to perform reasonable operations.

XI. Define the infinitive constructions and translate the sentences:

1. We know B. Pascal to be the first inventor of the mechanical computer. 2. B. Pascal is known to be the first inventor of the mechanical computer. 3. In the middle of the 17th century it was possible for B. Pascal to invent only the mechanical computer. 4. The possibility for the problem to be solved is illustrated by the given formula. 5. Human beings seem to be able to find facts or even logical consequence of facts in their memory according to association. 6. The magnetic recording is done on a disk which permits an information to be stored or read at one or several points on it. 7. The students were explained the high-speed memory unit to use the LSI circuits. 8. For results to be obtained an instruction has first been put into a computer.

XII. Translate the following sentences paying attention to the informs:

1. According to the principles of their work computers are subdivided into three parts: analog, digital, and hybrid. 2. When applying mathematical methods to the solving of technical problems engineers are most often interested in obtaining a finite numerical results. 3. Proper relation between theory and practice must be observed in training young specialists. 4. Mathematical tables are necessary aids (необходимые средства) for performing computational work. 5. The students get the practical training when they are working at various plants. 6. When performing the problems in mathematical practice, the students use desk calculators such as arithmometers, key computing machines and slide rules (логарифмическая линейка). 7. In modern computers LSI circuits and RAM/ROM memories are used for executing sophisticated (усложненный) operations. 8. A memory unit is used for storing information. 9. Electronics being used not only in industry but in many other fields of human activity as well, one should have an idea of what it is. 10. The processing of messages can be performed sequentially, i.e., a new task is not given until the current one is completed. 11. Having conducted many experiments scientists proved that electricity had an atomic character. 12. The fast electronic machines, such as microcomputers, are effective for carrying out complicated (сложный) computations.

XIV. Read Text В and translate it with a dictionary. Write a short summary:

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