The computer system consists of three main components:

  1.  Input Device
  2. Output Device
  3.  Central Processing Unit (CPU), and
  4.  Memory Unit.

The I/O unit consists of the input unit and the output unit. CPU performs calculations and processing on the input data, to generate the output. The memory unit is used to store the data, the instructions and the output information. The following figure illustrates the typical interaction among the different components of the computer.

1. Input Device: 

Input devices convert input data and instructions into the binary form for understand by the computer. There are different types of input devices like keyboard, Magnetic Ink Character Recognition (MICR), Optical Character Recognition (OCR), mark sense reader, etc.

2. Output Device: 

Output devices are that type of devices that receive information from the CPU and present this information to the user in the desired form. Output devices include display screen, printers, loudspeakers, plotters, etc.

3. CPU (Central Processing Unit):

The CPU has two parts that is Control Unit (CU) or Arithmetic Logic Unit (ALU). CPU is also known as the brain of a computer as it executes the program instructions.

  • Control unit (CU)
  • ALU (Arithmetic Logic Unit)

i) Control unit (CU)

The control unit of computer is tells that how the rest of the computer system carries out a program’s instructions. CU is directs to the movement of electronic signals between memory –that is temporarily holds instructions, data or processes information - and the ALU. ALU is also directs with these control signals between the CPU and the input/output devices.

ii) ALU (Arithmetic Logic Unit): 

ALU does two kinds of operations - arithmetical and logical. Arithmetical operations of ALU are the fundamental mathematical operations. These operations consist addition, subtraction, multiplication or division. Logical operations of ALU consist of comparisons. Logical type operation is two pieces of data these are use to compare to see whether one is equal to, less than or greater than the other one.

3. Memory Unit

Computer memory is the working storage part or area in the computer. There are two types of computer memory: primary memory and secondary memory.

  • Main Memory
  • Cache Memory
  • Register

i) Main Memory

RAM is the primary or main memory. It is volatile in nature and holds the data for a short period of time only, that is only until the system is running.

Files and instructions are saved in different secondary storage systems and they are fetched to the RAM before the execution. This technique is known as swapping. Memory space available in the main memory directly affects the speed of the computer.

ii) Cache Memory

It is the smallest and fastest form of memory. The contents that require to be fetched frequently are stored in the cache memory.

Therefore, the processor before looking for the content in RAM checks here and goes to RAM only if the content isn’t available here. Cache memory is always placed between RAM and the processor.

iii) Register

There are special-purpose temporary storage units which are called registers. They are the form of memory with the highest transfer speed.

These registers are used for holding instructions, data and intermediate results that are currently being processed. Examples: Program Counter (PC), Instruction Register, Memory Address Register, Memory Buffer Register, Memory Data Register, Accumulator, etc.