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Computer Architecture - Professional Knowledge

Published on Saturday, January 09, 2016
Hello Readers, 

We'll discuss basic computer architecture along with microprocessors. Use the comments section for doubts/clarifications!
Computer Architecture

This article is a part of PK Series(IT)

A basic computer system consists of the following components :-

1. CPU

Central processing unit is that core element of a computer system that carries out instructions of a computer program by performing basic arithmetic, logical, control and I/O operations. 

2. Memory

Every computer has 2 types of main memories - RAM and ROM

Random Access Memory can be read and written to anytime the CPU instructs it. Contents of RAM are erased when the computer is turned off whereas Read Only Memory is pre-loaded with data and software that never changes. ROM is typically used to store computer's initial start up instructions. 

3. I/O unit

I/P refers to the communication between a computer and outer world. Input are signals/data received by system and Output are signals sent by it. Peripheral devices provide input/output to the system. Peripherals include input devices like keyboard, mouse and output devices like display screen or printer. Hard disk and optical disk devices act as both input and output devices. 

Block diagram for basic computer architecture is given below:

Computer Architecture


It is a programmable integrated device which has the capacity of computing & decision making. It communicates with the system in binary numbers 0 &1. Every microprocessor has fixed set of instruction in the form of binary patterns known as machine language. 

Various components of a microprocessor are described below:

Arithmetic and Logical Unit (ALU)

It is the most important component of a microprocessor that performs the arithmetical and logical operations like AND, OR, NAND, NOR, Addition and Subtraction. 

Control Unit

Its the circuit that controls the flow of information through processor and coordinates the activities of other units within it. With a regular processor, control unit performs tasks of fetching, decoding, managing execution and storing results. 

Register Sets

Register sets temporarily store data and program codes until they are sent to ALU or control section. More registers per cpu results in programming tasks easily. Registers are measured by no of bits i.e 8 bit, 16 bit, 32 bit.


Its a register in which intermediate arithmetic and logical results are stored. Initially set to zero, each number after operation is added into it and finally results are sent to main memory or to another register. 

Condition Code Register (CCR)

Its an 8 bit register used to store the status of CPU such as carry, zero, overflow and half carry. 

Program Counter (PC)

Its a 16 bit register used to store the next address of the operation code to be fetched by CPU

Stack Pointer (SP)

Stack is a data structure that grows downward from high memory to low memory. SP holds the 16 bit address of the next free location in the stack. On a subroutine call or interrupt it pushes the return address and retrieves it when the operation is complete. 

Data Bus

A subsystem which transfer the data between different components of a computer. Its bi directional in nature and depending upon the microprocessor it can handle 8 bit or 16 bit data. 

Address Bus

It is unidirectional in nature over which microprocessor sends an address code to the memory or I/O. The more bits in an address bus enables microprocessor to access more locations. A 16 bit address bus is capable of handling 64K addresses. 

Control Bus

Control bus is used by microprocessor to send out or receive timing and control signals in order to coordinate and regulate its operation and to communicate with other devices. 

Microprocessor Clock

Its the speed at which microprocessor executes instructions, also called clock rate. Clock rate is expressed in MHz or GHz.

Block diagram for microprocessor is given below for further understanding:

Computer Architecture

8085 is an 8 bit microprocessor introduced by Intel in 1977 while 8086 is a 16 bit microprocessor chip by Intel only which gave rise to x86 architecture.

Interesting fact about India

The art of navigation and navigating was born in river Sindh over 6000 years ago. The very word 'navigation' is derived from Sanskrit word 'Navgatih'. The word navy is also derived from Sanskrit word 'Nou'.

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