GCD of two numbers:

XOR AX,AX

MOV AL,[1500h]

MOV BL,[1501h]

loc3: CMP AL,BL

JNC loc1

XCHG AL,BL

MOV AH,00h

loc1: DIV BL

XOR AH,00h

JZ loc2

MOV AL,AH

SUB AH,AH

JMP loc3

loc2: MOV [1504h],BL

HLT