Pentium Arcitecture

PENTIUM ARCHITECTURE:

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• REGISTER SET

• INSTRUCTION FORMAT

• ADDRESSING MODES

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REGISTERS:

The processor has 16 registers for use in general systems. These registers can be grouped as:

General purpose data registers:

• Eight registers are available for storing operands and pointers.

• These are EAX, EBX, ECX, EDX, ESI, EDI, EBP, and ESP.

• These are provided for holding operands for logic and arithmetic operations, operands for address calculations, memory pointers.

• The ESP register should be used very carefully. It holds the stack pointer and generally should not be used for any other purpose.

• There are some special uses of each register:

EAX: Accumulator for operands and result data.

EBX: Pointer to data in the DS segment.

ECX: Counter for string and loop operations.

EDX: I /O pointer

ESI: Pointer to data in the segment pointed to by the DS

register, source pointer for the string operation

EDI: Pointer to data or destination in the segment pointed to by

the ES register.

ESP: Stack pointer

EBP: Pointer to data on the stack (in the SS segment).

These extended 32-bit registers can be separately referred to as two 8-bit registers, so each of the EAX, EBX, ECX, EDX can be referred to as AH, BH, CH, DX (high byte) and AL,BL,CL,DL (low byte).The following figure shows the alternate general purpose register names .

Segment Registers:

• There are segment registers. CS, DS, SS, ES, FS, GS. They hold up to 16-bit segment selectors. A segment selector is a special pointer that identifies a segment