Learning 8086 Assembly Language: Environment Setup, Sample Program, Registers, Instruction Classification, and Execution Mechanism

Through a concise 8086 assembly language tutorial, readers gain low‑level programming experience and a deep understanding of how a machine executes programs.

Environment installation : Use VirtualBox with a DOS ISO or DOSBox; create a custom ISO (e.g., hdiutil makehybrid -o masm.iso ./mas ) and mount it. Useful links include the source code download page and an assembly forum.

Simple program example (shown below) demonstrates pseudo‑instructions (assume, segment, end), data and stack segments, and calls to subroutines for string length, case conversion, and reversal:

assume cs:code,ds:data,ss:stack

data segment
  db 'hello world'
  db 16 dup(0)
data ends

stack segment
  db 32 dup(0)
stack ends

code segment

start:      mov ax, data
            mov ds, ax
            call strlen ; BX = 0BH (11)
            call strtoupper ; convert to uppercase
            call strrev ; reverse string

      mov ax,4c00h
      int 21h

strlen:     mov bx, 0
s:     mov al, ds:[bx]
            cmp al, 0
            jne next
            ret
  next:     inc bx
            loop s

strtoupper: mov cx, bx
            mov si, 0
s1: mov dl, byte ptr [si]
            cmp dl, 65 ; 'A'
            ja next1
ss1:    mov byte ptr [16+si], dl
            inc si
            loop s1
            ret
  next1:    and dl,11011111b
            jmp ss1

strrev:     mov ax, stack
            mov es,ax
            mov cx, bx
            mov di, bx
            mov si, 0
            mov bx, data
            mov ds, bx
            mov bx, 16
s2:   mov al, ds:[bx+si]
            mov es:[di], al
            inc si
            dec di
            loop s2
            ret
code ends
end start

The program uses pseudo‑instructions (assume, segment, end), assembly instructions, and labels (code, data, s1).

General registers : AX, BX, CX, DX, SI, DI, SP, BP, IP, CS, SS, DS, ES, PSW.

Instruction classification is illustrated with diagrams (not reproduced here) showing categories such as data movement, arithmetic, control flow, etc.

Program execution : Physical address = segment × 16 + offset. Example segment:offset notation (SA+10H:0) is explained with references to textbook pages.

Data addressing and access : 8086 handles byte and word data; explicit byte ptr or word ptr is required for memory accesses without registers.

References: debugging guide (https://thestarman.pcministry.com/asm/debug/debug.htm) and a CSDN article (https://blog.csdn.net/weixin_43809545/article/details/103640185).