Question

I’ve started to learn asm, and I wondered what is the difference between these two different ways of using the MOV instruction into AL:

First:

MOV AL,5H

Second:

MOV SI,5H
MOV AL,[SI]

Answer 1

Those two do different things.

; let me use friendlier syntax; IMHO, lower case and 0x5 instead of 5h is more
; readable in case of assembly
mov al, 0x5 ; al = 0x5

mov si, 0x5 ; si = 0x5
mov al, [si] ; al = *si; that is, al is now what was in memory at address 0x5

There is easy wikibook about x86 assembly that will better explain the concepts and syntax to you: x86 Assembly. Assembly is generally easy language, but it’s best to just follow tutorial/book about it, to first fully understand syntax, and then – and only then – jump into wild world of assembly reading and writing.

Also, for other resources, you can look here.