Computer is a type of electronic machine or an electronic device which is given meaningless or uncoordinated data and instructions, it acts promptly on these instructions and also has a capacity to store them apart from presenting them in a more useful information form. In other words, an electronic device which automatically performs logical operation on the basis of input data or information provided on it and provides answers in output form according to the data or set of instructions already stored on it, is called a computer. Remember that word “computer” is a Latin word that means a computing or calculating device or machine. As such, a computer is a device, which receives information in an input form and infers different conclusions on the basis of this information. It performs all tasks in the light of specific programs stored in its memory and provides useful and meaningful information in output form.
A digital computer consists of the following five sections or units;
1). Input 2). Memory 3). Arithmetic 4). Control 5). Output
These five sections of a computer have been illustrated in figure 11.2. The arithmetic logic unit (ALU), memory unit, and control unit are basic elements of a microprocessor or central processing unit, has been illustrated by the figure.
The input devices of a computer include a keyboard, mouse, joystick, graphic tablet, card reader, magnetic tape unit, scanner, network connection or telephone line, etc. These devices transmit person-to-machine or machine-to-person information. Remember that every input device normally encodes human language to a computer language (i.e. the function of an input device is to provide important data and instructions on a computer in such a language, which it can comprehend)
A memory section is a storage place for data and programs (i.e. memory unit is a place inside a computer where data and programs are stored). Memory is an important part of a micro – processor or CPU. Every bit of information stored on memory has its own address or location. Initially, the major share of memory in a CPU consisted of a traditional magnetic cover memory, however now semi- conductor memories are being applied. Commonly used memory devices are magnetic covers, IC memories, magnetic drums, magnetic tapes, hard disks and floppy etc.
The arithmetic unit is a part of the central processing unit and as its name reflects, it performs all sorts of arithmetic operations e.g. addition, subtraction, multiplication, division, comparison, and some other logical operations etc. it is pretty obvious from the figure that a two – way exists between memory and arithmetic sections, which means that data can be transmitted on arithmetic section for action purposes and conclusions drawn as a result of this action, can also be stored back on memory. Arithmetic unit is also sometimes known as ALU (arithmetic logic unit).
The control system is similar to a nervous system or the brain of a computer. It passes instructions on other parts of the computer to operate properly and tells input as to when and where information has to be stored on memory. It directs memory to transmit information on the arithmetic section and directs the arithmetic section to receive this information and also to execute it (e.g. add it). It also directs the arithmetic section to transmit answers thus received back on to memory and output device. Further, it also instructs output device as to when it has to operate. Remember that control unit is a segment of CPU and a clock for computer. Its task is to receive appropriately organized stored information during a period of time and then proper execution of these instructions by means of other devices.
Output section is a link between machine and a person or machine and a device (i.e. computer’s output section, translates computer’s output in such a language that every person can understand it easily). In other words, output section is just similar to the input section except that operation of both sections is inverted (i.e. input section encodes human language and converts it to computer language whereas output section decodes computer language and converts it to human language). Some of the commonly used output devices are line printers, CRT monitor, television, speaker, plotters, laser printers, magnetic tape machine, card punching machine etc. Thus, output section can communicate with a person through a printer. It can provide output information on a CRT display. Output information can also be provided on bulk storage devices e.g. magnetic tape, disks or optical disks etc.
In figure 11.9, program instructions and data flow of a computer system has been illustrated. It is evident from the figure that two types of information are provided on a computer. One of this information consists of program (instructions) which tells control unit as to which procedure should be adopted for the solution of any problem or how to proceed ahead. This program, which a programmer writes or develops quite cautiously, is stored on the central memory at a time when problems are being solved. The other type of information being provided on a computer is data. Data consists of facts and figures which are required for the solution of any problem.
It must be inculcated that program information have been stored within the memory and can be used only through a control unit. Whereas data information is transmitted on different locations of a computer and execute by means of an ALU. Data does not require to move towards a control unit at all. Auxiliary memory is an extra memory which is required only to store partial conclusions of any complicated problem and it is not reflected on CPU. Remember, data can also be stored on peripheral devices e.g. hard drive.
Figure 11.9 – Flow of program instructions and data in a computer system
The operational mechanism of a computer is as follows;
Data and programs transfer on the computer’s main or internal or primary memory under directions from the control unit. During the execution of any given assignment, every program instruction restores from the memory in a proper sequence and the control unit elicits its definite meaning or translate it and informs ALU about the prospective operation going to be executed. It also directs simultaneously to transfer of necessary data from memory to ALU. ALU solves all calculations and transmits these conclusions to memory, where it gets stored temporarily before appearing on the output devices. Remember that this entire process takes place under the overall supervision of a control unit.
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