What is the difference between MOV and LEA?

assembly x86 instruction-set
naveen picture naveen · Nov 9, 2009 · Viewed 179.7k times · Source

I would like to know what the difference between these instructions is:

MOV AX, [TABLE-ADDR]

and 

LEA AX, [TABLE-ADDR]

Answer

Ruben Bartelink picture Ruben Bartelink · Nov 9, 2009
  • LEA means Load Effective Address
  • MOV means Load Value

In short, LEA loads a pointer to the item you're addressing whereas MOV loads the actual value at that address.

The purpose of LEA is to allow one to perform a non-trivial address calculation and store the result [for later usage]

LEA ax, [BP+SI+5] ; Compute address of value

MOV ax, [BP+SI+5] ; Load value at that address

Where there are just constants involved, MOV (through the assembler's constant calculations) can sometimes appear to overlap with the simplest cases of usage of LEA. Its useful if you have a multi-part calculation with multiple base addresses etc.

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