Compare two values and sets flags accordingly.
operand1 - operand2
result is not stored anywhere, flags are set (OF, SF, ZF, AF, PF, CF) according to result.
CMP REG,MEM CMP REG,REG CMP MEM,REG CMP MEM,IMMIDIATE
MOV AL, 5 MOV BL, 5 CMP AL, BL ; AL = 5, ZF = 1 (so equal!)