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Addressing Modes of Pentium Processor:

The Addressing Modes of Pentium Processor can support the following modes, namely

  • Register mode
  • Immediate mode
  • Register direct mode
  • Direct mode
  • Base displacement mode
  • Base indexed mode
  • PC relative mode

The effective address can be computed as

Effective address = Base Register + Index register x Scaling factor + displacement

where

  • base registers are EAX, EBX, ECX, EDX, ESP, and EBP
  • Index register is EDI, and ESI
  • Scaling factor is 1, 2, 4 and 8

For example, the addressing modes of Pentium Processor looks like

[EBX] [EDI x 2] +FF

Register Mode In this mode, the operand is in a register. For example, MOV EAX, EBX. The content of EBX register is copied to EAX register.

Register Direct Mode In this mode, the operand is in effective-address-use-register direct mode. For example, MOV EAX, [ESP]. The content of the EBX register is copied to the EAX register.

Immediate Mode In this mode, the operand is in the instruction. For Example, MOV EAX, 88.

Direct Mode In direct address mode, the effective address is within the instruction. For example, MOV EAX, address. The content of the effective address will be copied into the register EAX.

Base Displacement Mode The effective address is the sum of the contents of the register and a constant. For example, MOV EAX, [ESP+4]. The contents of memory location specified by the effective address must be copied into the EAX register.

BaseIndexed Mode The effective address is the sum of the contents of two registers. For example, MOV EAX, [ESP][ESI]. The contents of ESP and ESI registers are added to generate the effective address of the memory location. The content of the memory location specified by the effective address must be copied into the EAX register.

PC Relative Mode In this addressing mode, the effective address is computed by the sum of the contents of PC and a constant within the instruction. For example, JMP address. The contents of the program counter are added with an offset which is existing within the instruction. The computed result of addition is placed into the program counter (PC).