As it is known the two functional units of the CPU are the control unit (CU) and the arithmetic-logical unit (ALU). The control unit manages and coordinates the entire computer system. It obtains instructions from the program stored in main memory, interprets the instructions, and issues signals that cause other units of the system to execute them.
The control unit operates by reading one instruction at a time from memory and taking the action called for by each instruction. In this way it controls the flow between the main storage and the arithmetic-logical unit.
The control unit has the following components: a counter that selects the instructions, one at a time, from memory; a register that temporarily holds the instructions read from memory while it is being executed; a decoder that takes the coded instruction and breaks it down into individual commands necessary to carry it out; a clock, which produces marks at regular intervals. These timing marks are electronic and very rapid.
The sequence of control unit operations is as follows. The next instruction to be executed is read out from primary stor-
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age into the storage register. The instruction is passed from the storage register to the instruction register. Then the operation part of the instruction is decoded so that the proper arithmetic or logical operation can be performed. The address of the operand is sent from the instruction register to the address register. At last the instruction counter register provides the address register with the address of the next instruction to be executed.
The arithmetic-logical unit (AL U) executes the processing operations called for by the instructions brought from main memory by the control unit. Binary arithmetic, the logical operations and some special functions are performed by the arithmetical-logical unit.
Data enter the ALU and return to main storage through the storage register. The accumulator serving as a register holds the results of processing operations. The results of arithmetic operations are returned to the accumulator for transfer to main storage through the storage register. The comparer performs logical comparisons of the contents of the storage register and the accumulator. Typically, the comparer tests for conditions such as "less than", "equal to", or "greater than".
So as you see the primary components of the arithmetic-logical unit are banks of bistable devices, which are called registers. Their purpose is to hold the numbers involved in the calculation and hold the results temporarily until they can be tranferred to memory. At the core of the ALU is a very high-
105 Unit 8. Central Processing Unit
speed binary adder, which is used to carry out at least the four basic arithmetic functions (addition, subtraction, multiplication and division). The logical unit consists of electronic circuitry which compares information and makes decisions based upon the results of the comparison.
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9. , .
1. What are the functional units of CPU? 2. What is the function of CU? 3. How does CU operate? 4. What is the function of a counter? 5. What role does a decoder play? 6. What is the sequence of CU operations? 7. What is the function of the arithmetic-logical unit? 8. What operations are performed by ALU?
9. What primary components does ALU consist of? 10. What is
the function of an accumulator / comparer?
10.
:
; ; - ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; , ; ; ; ; ; ; ; .
. , .
Register, address register; base register; clock register; command / instruction register; counter register; CPU register; hardware register; input / output register; memory register; operand register; general-purpose register; special-purpose register.
Counter binary counter; character counter; data counter; instruction counter; pulse counter; sequence counter; storage counter; software counter; time-out counter.
Selection: color selection; directory selection; drive selection; file selection; function selection; keyboard selection; menu selection; security selection.
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Management: data management; database management; disk management; error management; information management; memory management; network management; resource management; task management; window management.
12. 1 2 ,
:
Verbs: to work; to control; to receive; to keep; to send; to perform; to demand; to choose; to supply; to pass; to name; to include; to apply; to come back; to found; to explain; to form; to define; to arrange.
Nouns: computer; answer; commands; memory; element; device; information; state; aim; heart; solution; computation.
Adjectives: main; whole; separate; quick; correct; large; main (storage); following; every; following; specific; different; real.
13. ,
.
.
1. Having returned to the accumulator the results of arith
metic operations are transferred to main storage. The results of
arithmetic operations are returned to the accumulator, the stor
age register transfering them to main mamory. The results of
arithmetic operations being returned to the accumulator, the
storage register transfer them to main memory. Being returned
to the accumulator the results of arithmetic operations are trans
ferred to main memory.
2. When passing through a conductor free electrons form an
electric current. Free electrons passing through a conductor, an
electric current is generated. Free electrons pass through a con
ductor, an electric current being generated. Free electrons pass
ing through a conductor form an electric current.
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3 Instructions being obtained, the control unit causes other units to perform the necessary operations. Instructions are obtained, the control unit causes other units to perform the operations. Having obtained the instructions the control unit causes other units to perform the operations. Obtaining the instructions the control unit causes other units to perform the operations.
4. The elements having unknown properties cannot be used for experiments. The elements have unknown properties, exper-
107_________________________ Unit 8. Central Processing Unit
iments with these elements being impossible. Having unknown properties the elements cannot be used for experiments. The elements having unknown'properties, experiments with them are impossible.
5. When moving in a material charged particles ( ) produce magnetic properties () of this material. Charged particles moving in a material produce magnetic properties. Charged particles moving in a material, magnetic properties of this material are produced. Charged particles move in a material, magnetic properties of the material being produced.
14. . , , .
** cjK
It is known that one of the fundamental parts of the computer is a control unit. This unit controls the computation process automatically, without man's participation. It sends signals to all other parts of the computer to specify what they must do. First of all, the control unit tells the main memory what data must be transferred to the arithmetic-logical unit and other devices. Then it enables the arithmetic-logical unit to perform the required operation. Finally, it places the obtained results in the main memory.
It is important to note that the control unit operation is determined by an algorithm of a problem solution. The algorithm is a sequence of arithmetic and logical operations. These operations must be performed on the initial data for solving the problem.
Description of an algorithm in a form acceptable by a computer is called a program. A program is a list of sequential computer instructions enabling a computer to solve a problem. In order to be acceptable by the computer instructions must be encoded into a digital form.
In conclusion it should be pointed out that the main feature of a computer is automatic control of the problem solution process. It is based on the programmed-control principle.
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15. . .
* * #
1. In 1960's advances in microelectronic components led to
the development of the minicomputer, followed more recently
by an even smaller microcomputer. Both have filled a need for
small but relatively flexible processing systems able to execute
comparatively simple computing functions at lower costs.
In 1971 Intel Corporation delivered the first microprocessor, the 4004. All the logic to implement the central processing unit of a tiny computer was put onto a single silicon chip less than 1/4 inch square. That design was soon followed by many others. The progress toward smaller computers is continuing, designers are working at nano-computers and pico-computers.
When the central processing unit of a computer is implemented in a single, or very small number of integrated circuits, we call it a microprocessor. When a computer includes a microprocessor as its major component, such device is called a microcomputer.
Today the hardware in data-processing machines is built out of microelectronic devices. Advances in microelectronic devices give rise to advances in data-processing machinery.
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2. The computer has made it possible to mechanize much
of the information interchange and processing that constitute
the nervous system of our society.
The versatility and convenience of the microprocessor has changed the entire architecture of modern computer systems. No longer is the processing of information carried out only in the computer's central processing unit. Today there is a trend toward distributing more processing capability throughout a computer system, with various areas having small local processors for handling operations in those areas.
There are a number of advantages of distributed processing. First,.since many elements of the computer can be working on different portions of the same task, the work may be done faster. Second, if one element in the network malfunctions, its workload can be shifted to another element or shared among several elements, so that the entire work is relatively immune
109 Unit 8. Central Processing Unit
to failure. Third, the network can be small enough to be contained within a single laboratory or building, or it can be spread out over a wide area.
TESTS
1. .
1. Programs and data to be processed must be in the____________
memory.
,a) internal; b) external; c) secondary
2. The control unit_________ instructions from the program.
a) sends; b) changes; c) obtains
3. The results of arithmetic operations are returned to the
_____ for transferring to main storage.
a) decoder; b) counter; c) accumulator
4. The instruction to be__________ in control unit is read out
from primary storage into the storage register.
a) calculated;Jb) executed; c) read out
5. The______ performs logical comparisons of the contents
of the storage register and the___________.
a) adder; b) accumulator; c) comparer
6. The read out command is passed from the____________ regis
ter to the________ register.
a) instruction; b) address; c) storage
7. CPU is designed to________ and to_______ basic instruc
tions for the computer.
/a) control; b) consist; c) carry ouU
8. CU and ALU consist of electronic circuits with millions
of______.
a) sensors; b) servers; c) switches
2. ,
.
1. CPU f/- -a) performs the processing operations;
2. CU ^ -b) carries out logical comparisons of stor-
age;
3. ALU -) executes basic arithmetic functions;
4. accumulator; d) coordinates the operation of the whole
system;
