Introduction

  • In computer architecture, a processor register is a very fast computer memory used to speed up the execution of computer programs by providing quick access to commonly used values.

Definition

Features

  • Register are used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU.
  • Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only.
  • Registers are typically addressed by mechanisms other than main memory.
  • A processor register may hold an instruction, a storage address, or any data (such as bit sequence or individual characters).
  • The computer needs processor registers for manipulating data and a register for holding a memory address.
  • The instruction execution is performed in the CPU registers.
  • It is the temporary storage location in CPU for program execution.

Types of CPU/Processor Register

(A) There are various types of Registers those are used for various purpose – 

    • Accumulator Register (AC):
      • This is the most frequently used register used to store data taken from main memory.
      • This register is used to store data temporarily for computation by ALU.
      • AC is considered to contain one of the operands.
      • It is a general purpose processing register.
      • The result after computation by ALU is also stored back to this AC.
      • It is present in different numbers in different microprocessors.
    • Memory Address Registers (MAR):
      • It holds the address of memory location from which data or instruction is to be accessed/fetched (read operation) or to which the data is to be stored (write operation).
    • Memory Buffer Registers (MBR):
      • It is a register, which contains the data to be written in the memory (write operation) or it receives the data from the memory (read operation).
    • Program Counter (PC):
      • It keeps track of the instruction that is to be executed next, that is, after the execution of an on-going instruction.
      • Program Counter (PC) is used to keep the track of execution of the program.
      • It contains the memory address of the next instruction to be fetched. PC points to the address of the next instruction to be fetched from the main memory when the previous instruction has been successfully completed.
      • Program Counter (PC) also functions to count the number of instructions.
    • Instruction Register (IR):
      • The instruction read from memory is placed in the Instruction register (IR) which is currently been executed.

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