Explanation of Block Diagram of Computer|Computer Notes

  • Connection of 8 or more wires through which data bits can flow at once.
  • It can handle large amount of data.

Serial Port:

  • Data bits can flow one at a time.
  • It can handle less data than Parallel port.


  • High-speed memory inside the CPU.
  • Very small in size.
  • Temporary storage for memory Addresses and Instructions during the execution of the program.
  • Read and execute the instructions.
  • Processing speed depends upon the size of register.
  • Some common registers are
  1. Instruction Register (IR) Stack Register (SR)
  2. Memory Address Register (MAR) Program Counter (PC)
  3. Memory Buffer Register (MBR)

Instruction Register (IR):

Holds an instruction that is being executed.

Stack Register (SR):

It is a part of CPU, in which data is store and retrieved.

Memory Address Register (MAR):

Holds the address of the active memory location.

Program Counter (PC):

Holds the memory address of the instruction that is next to be executed.

Memory Buffer Register (MBR):

Holds data on its way to and from memory.


Three types of system software are

  1.   Operating Systems
  2. Operating Environment
  3. Utilities

Operating Systems

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