2 The “mov” instruction

Before we can discuss addressing modes, it is important to start with an instruction. It is natural to choose the mov instruction because it does not involve any computation, and yet it has a source and a destination operand.

In general, a mov instruction looks like the following:

This is a typical syntax description that is also used to describe the syntax of many other languages. Here is a quick explanation:

• Regular text like mov are required verbatim.
• Anything enclosed by square brackets ([]) is optional.
• Alternatives are separated by the vertical bar (|).
• Place holders to be replaced by something else are enclosed by angle brackets (<>).

As a result, in this case, the instruction itself can be mov, movb, movw or movl. It must have two operands, <src> and <dest>. The two operands must be separated by a comma. An operand of an instruction is like arguments of a function. Operands supply extra information that is needed for an instruction to execute.

Note that the mov mnemonic is actually a misnomer. It should have been cpy for copy. This is because memory content is not moved, but rather copied. In other words, the <src> still retains the same value after a mov instruction.