Intel-32 Architecture

Families - x86

• 8088, 8086

  →16 Bit registers

  → AX, BX, CX, DX, SI, DI, BP, SP, CS, DS, SS, ES, IP

• 80286

  → Protected Mode - OS runs in protected mode

  → Program cannot access other process’s space.

• 80386

  → Added 32 bit mode

  → Extends the registers. EAX, EBC, ECX.... etc

• 80486

  → Faster

Register → Registers are a type of computer memory used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU. Metaphorically, they can be seen as variables which will be used to store values in them and use later. Flags → The FLAGS register is the status register that contains the current state of a CPU

Registers

• General Purpose Register

• Segment Register

• Flags, EIP

• Floating Point Unit Registers

• MMX Register

• XMM Register

8 General Purpose

• EAX

• EBX

• ECX

• EDX

• ESI

• EDI

• ESP

• EBP

They are 32 bit

We can break register and access them in lower size.

• EAX → 32 Bit

• AX → Low 16 Bits of EAX

• AL → Low 8 bits of AX

• AH → High 8 bits of AX

Common functionality of them-

EAX → Accumulator

ECX → Counter for loops

EDX → EAX Multiply and Divide

ESI → Source Index

EDI → Destination Index

EBP → Base Pointer

ESP → Stack Pointer

EIP → Instruction Pointer. Points to current instruction to be executed.

Segment Register CS → Code segments DS → Data segments SS → Stack segment ES, FS, GS → Extra segments.

Memory model dependent (flat or segmented)

Flags register

They store info about a previous instruction that was executed.

CF → Carry Flag ZF → Zero Flag OF → Overflow Flag

FPU (Floating Point)

-x87 -They are 80 Bits -Behave like Stack

SIMD (Extensions) -MMX -SSE -SSE2 -SSE3

CPU Mode & Memory Management

I-32 have 3 mode -Real Mode (Only 1MB Memory access, no memory protection, Privilege not possible) -Protected Mode (Upto 4GB Memory, memory protection/privilege etc) -System Management Mode (power management tasks)

Memory Model Flat Model Segmented Model Real address Model

Memory Diagram

Here, Text section contains Executable code.

Initialized Data is .data section containing Initialized data. Whereas Uninitialized data is .bss section containing Uninitialized data.