The registers are the fastest accessible memory for the CPU. Normally, each core of a CPU has its own set of registers. The most used architectures are x86-32, x86-64 (for Desktop PC’s) and A32, A64 (for Embedded Devices).
| Instruction Set | x86-16 | x86-32 | AMD64/x86-64 | A32 | A64 |
|---|---|---|---|---|---|
| General Purpose | AX – DX, SI, DI | EAX – EDX, ESI, EDI | RAX – RDX, RSI, RDI, R8 – R15 | R0 – R10 | X0 – X15, X18 – X28 |
| Segment Register | CS, DS, SS, ES | CS, DS, SS, ES, FS, GS | CS, DS, SS, ES, FS, GS | – | – |
| Base Ptr. / Frame Ptr. |
BP | EBP | RBP | R11 (FP) | X29 (FP) |
| Intra Procedure | – | – | – | R12 | X16, X17 |
| Stack Pointer | SP | ESP | RSP | R13 (SP) | SP |
| Link Register | – | – | – | R14 (LR) | X30 (LR) |
| Instr. Ptr. / Progr. Counter |
IP | EIP | RIP | R15 (PC) | PC |
| Manufacturer | Intel | AMD/Intel | ARM | ||