UNIT - I BASIC STRUCTURE OF COMPUTERS
A computer consists of five functionally independent main parts. They are, ➢ Input
➢ Arithmetic and logic
➢ Control unit
Basic functional units of a computer
The operation of a computer can be summarized as follows
The computer accepts programs and the data through an input and stores them in the memory.The stored data are processed by the arithmetic and logic unit under program control.The processed data is delivered through the output unit.All above activities are directed by control unit.The information is stored either in the computer’s memory for later use or immediately used by ALU to perform the desired operations.Instructions are explicit commands that ▪ Manage the transfer of information within a computer as well as between the computer and its I/O devices. ▪ Specify the arithmetic and logic operations to be performed. To execute a program, the processor fetches the instructions one after another, and performs the desired operations. The processor accepts only the machine language program. To get the machine language program, Complier is used.
Note: Compiler is software (Translator) which converts the High Level Language program (source program) into Machine language program (object program) 1.Input unit:
The computer accepts coded information through input unit. The input can be from human operators, electromechanical devices such as keyboards or from other computer over communication lines.
Examples of input devices are
Keyboard, joysticks, trackballs and mouse are used as graphic input devices in conjunction with display. Microphones can be used to capture audio input which is then sampled and converted into digital code for storage and processing. Keyboard
• It is a common input device.
• Whenever a key is pressed, the corresponding letter or digit is automatically translated into its corresponding binary code and transmitted over cable to the memory of the computer. 2.Memory unit:
Memory unit is used to store programs as well as data. Memory is classified into primary and secondary storage. Primary storage:
It also called main memory.
It operates at high speed and it is expensive.
It is made up of large number of semiconductor storage cells, each capable of storing one bit of information.
These cells are grouped together in a fixed size called word. This facilitates reading and writing the content of one word (n bits) in single basic operation instead of reading and writing one bit for each operation Each word is associated with a distinct address that identifies word location. A given word is accessed by specifying its address.
The number of bits in each word is called word length of the computer. Typical word lengths range from 16 to 64bits.
Programs must reside in the primary memory during execution. RAM:
It stands for Random Access Memory. Memory in which any location can be reached in a short and fixed amount of time by specifying its address is called random-access memory. Memory access time
• Time required to access one word is called Memory access time. • This time is fixed and independent of the word being accessed. • It typically ranges from few nano seconds (ns) to about 100ns. Caches
They are small and fast RAM units.
They are tightly coupled with the processor.
They are often contained on the same integrated circuits(IC) chip to achieve high performance. ]Secondary storage:
It is slow in speed.
It is cheaper than primary memory.
Its capacity is high.
It is used to store information that is not accessed frequently. Various...
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