In the 8086 microprocessor, the stack is a special region of memory used for temporary storage of data, addresses, and status information, especially during subroutine calls, interrupts, and context switching.

What Is the Stack in 8086?
The stack operates on the LIFO (Last In, First Out) principle — the last item pushed onto the stack is the first to be popped off.

Structure of the Stack in 8086

• Segment Register: SS (Stack Segment)
• Offset Register: SP (Stack Pointer)
• Effective Address: SS:SP

The physical address of the stack top = SS × 16 + SP

How the Stack Works
PUSH instruction

• Decreases SP by 2 (8086 is a 16-bit processor).
• Stores a 16-bit value at SS:SP.

POP instruction

• Retrieves the value from SS:SP.
• Increases SP by 2.

CALL instruction

• PUSHes the return address onto the stack.
• Jumps to the subroutine.

RET instruction

• POPs the return address from the stack.
• Jumps back to that location.

Example: PUSH and POP

asm

MOV AX, 1234h
PUSH AX        ; AX is saved on the stack
; ... some code
POP BX         ; BX = 1234h

Important Notes

• Stack grows downward in memory (SP decreases as data is pushed).
• It must be initialized properly using:

asm

MOV SS, 7000h
MOV SP, 0FFF0h

• Stack overflows if SP moves below the reserved stack area — may corrupt program data.

Common Uses of the Stack