Computer Architecture

The first microprocessor chip was invented by Dr. Ted Hoff of Intel Corporation (USA) in 1969 and it become commercially available in 1971. It is a chief component of computer, without microprocessor computer is not computer but only pile of electromechanical, electronic and plastic materials beautifully connected to each other.

The working mechanism of computer is not simple, it is a complex machine so, it’s working mechanism is also very complex for new comers. Here, only summery of working mechanism is presented in simple words:

  • Main memory, ALU and control unit is main part of CPU. All input data is stored in main memory. The keyboard is a standard input device. When we input data through it, data is stored in buffer storage of keyboard, until enter key is not pressed.
  • Data come to ALU for processing, after processing, data is returned back to main memory. Main memory is a used as dark room of theater where actors/ actress are masking themselves before going to stage and return back again after finishing their performance.
  • From main memory, data go to secondary memory (Floppy, Hard Disk etc) for permanent storage or may directly to go printer for hard copy.
  • We take data or any information from secondary memory. These data may be processed in ALU then either return to secondary memory or go to output unit.
  • The control unit controls ALU, main memory, input/ output unit, secondary memory and other peripherals.
  • ALU contains internal memory (Registers). In this unit, all type of mathematical and logical data processing is successfully completed. It is used to perform several operations:
Arithmetic Logic Operation


Addition, Subtraction, Multiplication, Division, Increment, Decrement etc

Logical AND, Logical OR, Logical NOT, Logical EXCLUSIVE OR

Left Shift

Right Shift


Exponential, logarithmic, trigonometric and floating-point operations are not done by ALU. Special purpose math processor called FPU (Floating-Point Unit) Performs these operations. Now a day, on board FPU is used.





Function of ALU:.

(a) It accepts operands from registers.

(b) It performs arithmetic and logical operations.

(c) It returns results to register or a memory.

(d) The status of an ALU operation (negative, carry, zero, overflow) is available for writing into Flags register (FL).

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