Basic Computer Registers and Memory

A basic computer uses many register for different purpose. Some registers hold instructions, some decode the instructions and computer registers like accumulator will execute the instruction with operands or data provided by data register. All of these work together and help in various operations of the computer.

We have a list of computer registers given below, also, you may find detailed information in any computer architecture books. Each of the register has a symbol that is commonly used instead of its full name. The register also has a bit size – the number of bits of data or instruction it can hold.This is totally machine dependent as to how many bits it supports.

You will find 8-bit registers, 16-bit registers and 32-bit or a word registers, all equipped to handle complex instructions.

List of Registers in a Basic Computer (Image source: Computer Architecture by Morris Mano)
List of Registers in a Basic Computer (Image source: Computer Architecture by Morris Mano)

The primary functionality of each computer registers is given below. Each register is related to other in such a way that it pass instructions code or data to other registers.

DR - The data register holds the operand read from memory.

AC - The accumulator register is a general purpose processing register.

IR - Instruction from memory is placed in IR.

PC - It holds the address of next instruction.

TR - It holds the temporary data during processing of data.

AR - Holds address in 12 bit for operand.

Computer Registers Organization

The registers work together and they are organized in a particular way. See the figure below to understand their relationship. Each of the box is colored to show the affinity of a register to others registers, all single colored are directly related.

 ( Image source: Computer Architecture by Morris Mano)
( Image source: Computer Architecture by Morris Mano)

You can see that the memory units are kept separate and the accumulator which a type of register perform computation provided by data registers (operands), so they are kept together.

The rest of the registers are used for fetching, reading and decoding instruction. This is what is called the fetch-decode-execute cycle.



Mano, M. Morris. 1984. Digital Design. Pearson.

Mano, Morris. 1976. Computer System Architecture. Prentice Hall.