General Purpose registers are used for temporary storage of data and memory access. Since the processor accesses register more quickly than memory. 8086 has four 16-bit general-purpose registers AX, BX, CX and DX. These are available to the programmer, for storing values during programs. Each of these can be divided into two 8-bit registers such as AH, AL; BH, BL; CL, CH and DL, DH. Beside their general use, these registers also have some specific functions.

• AX Register (16-Bits): It holds operands and results during multiplication and division operations. All IO data transfers using IN and OUT instructions use A register (AL/AH or AX). It functions as accumulator during string operations.

Example:

MUL BL ; AX = (AL × BL)

MUL BX ; DX-AX = (AX × BX)

MUL BYTE PTR [BX] ; AX = (AL x DS:[BX])

• BX Register (16-Bits): It holds the memory address (offset address), in Indirect Addressing modes.

Example:

MOV CL, [BX] ; Moves a byte from the address pointed by BX in Data Segment into CL. Physical Address calculated as DS * 10H + BX

MOV CH, [BX+6] ; Moves a byte from the address pointed by BX+6 in Data Segment to CH; Physical Address: DS * 10H + BX + 6H

MOV CL, [BX+SI] ; Moves a byte from the address pointed by BX+SI in Data Segment to CL. Physical Address: DS * 10H + BX + SI

• CX Register (16-Bits): It holds count for instructions like: Loop, Rotate, Shift and String Operations.

Example:

MOV CX, 40H

BACK: MOV AL, BL

ADD AL, BL

. . MOV BL, AL

LOOP BACK

MOV CX, 40H BACK: MOV AL, BL ADD AL, BL . . MOV BL, AL LOOPZ BACK

• DX Register (16-Bits): It is used with AX to hold 32 bit values during Multiplication and Division. It is used to hold the address of the IO Port in indirect IO addressing mode.

Example:

MUL BX ; DX-AX = (AX × BX)

MOV DX, 2000H

IN AL, DX