Registers

Main x86 and x64 registers

There is 8 General Purpose Registers (GPRs) in x86 and x64 architectures.

x86	x64	name	Usage
EAX	RAX	Accumulator	Store the results of arithmetic and logical operations
EBX	RBX	Base	Store the base address of memory operands
ECX	RCX	Counter	Store the count of iterative instructions
EDX	RDX	Data	Store the results of multiplication and division operations
ESP	RSP	Stack Pointer	Store the stack pointer
EBP	RBP	Base Pointer	Store the base pointer
ESI	RSI	Source Index	Store the source index for string operations
EDI	RDI	Destination Index	Store the destination index for string operations

Two groups are distinguished :

• EAX/RAX, EBX/RBX, ECX/RCX and EDX/RDX have to store temporary data for the processor.

• ESP/RSP, EBP/RBP, ESI/RSI and EDI/RDI are instead used as pointers and indexes

There is three other main registers :

x86	x64	Name	Usage
EFLAGS	RFLAGS	Flags	Store the current state of the CPU's flags, which are special bits that are used to control the execution of instructions
EIP	RIP	Instruction Pointer	Store the current instruction pointer, which is the address of the next instruction to be executed by the CPU. The instruction pointer is automatically updated by the CPU as instructions are executed, and it is used to determine the order in which instructions are executed
CS	CS	Code Segment	Store the code segment selector, which is a value that specifies the current segment of memory that is being used to store the instructions that are executed by the CPU

There is other registers like the segment registers (DS, ES, FS, GS, and SS), the control registers (CR0, CR1, CR2, CR3, and CR4), and the debug registers (DR0, DR1, DR2, DR3, DR4, DR5, DR6, and DR7). However, this is not a complete list, and there may be other registers that are available on some 32-bit x86 CPUs.