x86 Registers 32-bit

General-purpose Registers:

The 80386 introduced 32-bit versions of the general-purpose registers, which can now hold 32-bit values.

1. EAX (Extended Accumulator Register): Used for arithmetic operations, logic operations, and I/O. It is split into:

   • AH (high byte)

   • AL (low byte)

   • AX (16-bit version of the register)

2. EBX (Extended Base Register): Used for addressing and data manipulation. It is split into:

   • BH (high byte)

   • BL (low byte)

   • BX (16-bit version of the register)

3. ECX (Extended Count Register): Often used for loop counters and string operations. It is split into:

   • CH (high byte)

   • CL (low byte)

   • CX (16-bit version of the register)

4. EDX (Extended Data Register): Used in input/output operations and arithmetic extensions. It is split into:

   • DH (high byte)

   • DL (low byte)

   • DX (16-bit version of the register)

Index Registers:

The 80386 retains the 16-bit index registers but now supports 32-bit addresses.

1. ESI (Extended Source Index): Used as a pointer for string operations and memory addressing.

2. EDI (Extended Destination Index): Used as a pointer for string operations and memory addressing.

Segment Registers:

The 80386 continues to use segment registers, but these are now able to work in 32-bit mode.

1. CS (Code Segment): Points to the segment containing the current code.

2. DS (Data Segment): Points to the segment containing data.

3. SS (Stack Segment): Points to the segment containing the stack.

4. ES (Extra Segment): Used for string operations or as an additional data segment.

5. FS and GS: These two new segment registers were introduced with the 80386. They can be used for additional data segments or for specific purposes like pointing to specific memory areas for operating system and application data.

Pointer Registers:

1. ESP (Extended Stack Pointer): Points to the top of the stack and works with the 32-bit stack in protected mode.

2. EBP (Extended Base Pointer): Primarily used for referencing local variables and function parameters in the stack.

Program Counter:

1. EIP (Extended Instruction Pointer): Holds the offset address of the next instruction to be executed in the current code segment. It is a 32-bit register.

Flags Register:

The FLAGS register on the 80386 is 32 bits wide, unlike the 16-bit FLAGS register on earlier processors like the 8086. The FLAGS register contains various status and control flags, divided into two parts:

• EFLAGS: The 32-bit extended flags register, containing:

  • Status flags: These include the Zero Flag (ZF), Carry Flag (CF), Sign Flag (SF), and others, which indicate the results of arithmetic and logical operations.

  • Control flags: These control the operation of the processor, including Interrupt Enable (IF), Direction Flag (DF), and others.

  • System flags: Used for processor status, including the I/O privilege level, nested task flag, and virtual mode flag.

Debug Registers:

The 80386 also includes debug registers for debugging and tracing program execution:

1. DR0–DR7: Debug registers that can hold breakpoints for debugging operations.

Control Registers:

The 80386 introduces several control registers to handle memory management and system-level operations in protected mode:

1. CR0 (Control Register 0): Controls the state of the processor, including the enabling or disabling of protected mode and paging.

2. CR1 (Control Register 1): Not used in most systems; reserved for future extensions.

3. CR2 (Control Register 2): Holds the linear address that caused a page fault exception.

4. CR3 (Control Register 3): Contains the physical address of the page directory used for paging.

System Registers:

1. GDTR (Global Descriptor Table Register): Holds the base and limit of the Global Descriptor Table (GDT).

2. IDTR (Interrupt Descriptor Table Register): Holds the base and limit of the Interrupt Descriptor Table (IDT).

3. LDTR (Local Descriptor Table Register): Holds the base and limit of the Local Descriptor Table (LDT).

4. TR (Task Register): Points to the task state segment (TSS) for task switching.

Summary of 80386 Registers:

• General-purpose registers: EAX, EBX, ECX, EDX (32-bit versions), and their 16-bit counterparts (AX, BX, CX, DX, etc.).

• Index registers: ESI, EDI (32-bit versions).

• Segment registers: CS, DS, SS, ES, FS, GS.

• Pointer registers: ESP, EBP.

• Program counter: EIP.

• Flags register: EFLAGS (32-bit).

• Control and debug registers: CR0, CR1, CR2, CR3, DR0–DR7, and system registers (GDTR, IDTR, LDTR, TR).

The Intel 80386 greatly expanded the processor's capabilities compared to its predecessors, allowing for efficient handling of multitasking, virtual memory, and more complex applications.