15 - Instructions

Question 1

How long can x86 instructions be ?

Answer 1

From 1 to 15 bytes

Question 2

What three pieces of information do almost all instructions of BINARY codes contain ?

Answer 2

• The action/operation of the instruction
• The operands
• Where the result will go

Question 3

What three pieces of information do almost all instructions of MACHINE codes contain ?

Answer 3

– The operation required eg ADD, CMP, MOV
– The location of operands and results, ie the destination and source of eg AX, BX
– The data types of the operands

Question 4

Types of addressing modes ?

Answer 4

• Immediate (operand) mode: mov eax, 104
• Regiser: mov eax, ebx
• Direct: add eax, a
• Register indirect: mov eax, [ebx]
• Indexed Register Indirect with displacement: mov eax, table[ebx]