15. Operand Addressing Mode Types

• Instructions work on sources of data called operands.

• Here are the Operand Types and corresponding Addressing Modes:

  • Register - an 8-bit or 16-bit register on the 8086–80486, 32-bit on the 80386/486/Pentium.

  • Immediate - a constant value contained in the instruction itself.

  • Direct memory - a fixed location in memory.

  • Indirect memory - a memory location determined at run time by using the address stored in one or two registers.

• Instructions that take two or more operands always work right to left:

  • mov destination, source

• The right operand is the source operand.

  The source specifies data that will be read, but not changed by the intruction.

• The left operand is the destination operand.

  It specifies the data that will be acted on and possibly changed by the instruction.