What is an effective address?

Question

While reading the Intel 64 and IA-32 Architectures Software Developer’s Manual, the operation section for the LEA instruction (load effective address) uses a calculation called

Answer 1

Section 3.7.5 (Specifying an Offset) of the same document states:

The offset part of a memory address can be specified directly as a static value (called a displacement) or through an address computation made up of one or more of the following components:

• Displacement — An 8-, 16-, or 32-bit value.
• Base — The value in a general-purpose register.
• Index — The value in a general-purpose register.
• Scale factor — A value of 2, 4, or 8 that is multiplied by the index value.

The offset which results from adding these components is called an effective address. Each of these components can have either a positive or negative (2s complement) value, with the exception of the scaling factor.

EffectiveAddress calculates an effective address using:

Base + (Index*Scale) + Displacement