Registers

Computer Registers

Registers are a type of computer memory used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU. The registers used by the CPU are often termed as Processor registers.

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 register holding the memory location is used to calculate the address of the next instruction after the execution of the current instruction is completed.

Following is the list of some of the most common registers used in a basic computer:

Register	Symbol	Number of bits	Function
Data register	DR	16	Holds memory operand
Address register	AR	12	Holds address for the memory
Accumulator	AC	16	Processor register
Instruction register	IR	16	Holds instruction code
Program counter	PC	12	Holds address of the instruction
Temporary register	TR	16	Holds temporary data
Input register	INPR	8	Carries input character
Output register	OUTR	8	Carries output character

The following image shows the register and memory configuration for a basic computer.

• The Memory unit has a capacity of 4096 words, and each word contains 16 bits.
• The Data Register (DR) contains 16 bits which hold the operand read from the memory location.
• The Memory Address Register (MAR) contains 12 bits which hold the address for the memory location.
• The Program Counter (PC) also contains 12 bits which hold the address of the next instruction to be read from memory after the current instruction is executed.
• The Accumulator (AC) register is a general purpose processing register.
• The instruction read from memory is placed in the Instruction register (IR).
• The Temporary Register (TR) is used for holding the temporary data during the processing.
• The Input Registers (IR) holds the input characters given by the user.
• The Output Registers (OR) holds the output after processing the input data.