Computer Knowledge - Exam Oriented
1. Internal Parts & Working of Computers
A computer system comprises of central processing unit (CPU), [which itself comprises of Arithmetic and Logic Unit (ALU), main memory, and control unit], auxiliary or secondary storage, input and output devices.
The Main memory is also known as internal memory or primary storage. It is very fast in operation. It may be either core type which retains information even on supply failure, but is large in size, consumes more power and is relatively slow, or semiconductor type which is volatile, but fast and occupies less space. it contains a part of the operating system software one or more execution programs being executed, the data being processed and required by the programs for execution, and processed data awaiting output.
The control unit of CPU is the nerve centre as it controls and co-ordinates all the operations and input/output devices. It is a functional unit of a digital computer which calls up the individual commands of a program in a defined order, decodes them and initiates the required operation to be carried out by appropriate control signal. The data instructions pass in and out of the main memory via, memory data register (a special register which holds them temporarily). The machine instructions being currently interpreted are also held in a Special register called control instruction register. Control Unit stores the program in the memory, takes instructions one by one, interprets them and issues appropriate commands to the other units. It also transfers the results from ALU to the memory and then to the output device.
The ALU, unit of a digital computer is a section which performs all arithmetic comparisons like addition, subtraction, multiplication, division, etc., and data manipulation by logic actions based on AND and OR functions, shifting, rounding off and comparisons. A control console (comprising of video display unit for observing data/output from computer) and a Keyboard/Mouse for operator to interact with computer is also provided.
ALU also contains a number of accumulators and registers. It derives the desired data from the main memory as directed by control unit based on program fed. The data to be manipulated gets loaded into the accumulators. The result of arithmetic operation On data as per instruction is placed in the main storage or retained in the accumulator for further calculations.
Decision making quality of the computer is achieved by the capacity of ALU to perform logical operations.
The auxiliary memory or secondary storage is closely linked with the main memory of the CPU. Since main memory can�t be flooded with unwanted data at particular moment, same is stored in auxiliary memory from which desired data is fed to main memory as and when required by it. Thus secondary storage is used to hold mass of information i.e. system software and application programs not currently required in main memory and the data files. Obviously the capacity of secondary storage is very high compared to main memory or primary storage.
Auxiliary memory is usually in the form of magnetic discs, magnetic tapes, floppy disks or diskettes, fixed/moveable disk, Winchester disk, magnetic bubble memory, charged coupled devices, etc. and in some cases even solid state type is used as auxiliary memory. However non-volatile memory is preferred for auxiliary memory, i.e. its contents should not get washed on supply failure. Solid state memory and charged-coupled device type are volatile type of memories.
Before data is fed into input unit, it has to be properly prepared so that it is in machine readable form. This work is done by Data Preparation Equipment which may be in the form of card punch, or key disk system. In both these equipment data is captured by manual operation from the document. This process is time Consuming, expensive and error prone. To overcome these problems, now-a-days use is made of terminal (YDU and keyboard). It converts the data directly in machine-readable form as the data is entered, thus avoiding manual data conversion.
Input devices (like Keyboards, Mouse, punched card readers, paper tape readers, magnetic tape, magnetic disk, floppy disk, teletype writer terminal, optical scanners (optical mark reader, optical character reader), magnetic ink character reader, visual display unit, voice data entry terminal,mic etc.) read the machine-readable input medium prepared by data preparation equipment and feed it into the internal memory for processing, writing on secondary storage, or output.
Output device (like Monitor, printers, mag tapes, flopy disks, optical printers, laser printers, typewriters and visual displace devices, graph plotters, speakers etc.) are used to provide soft or hard copy of the desired information from the computer.
