The stack pointer rsp (esp for 32-bit machines) is used to point to the current top of the stack and should not be used for any other purpose other than in instructions which involve stack manipulation.

The base pointer rbp (ebp for 32-bit machines) is the twin brother of the stack pointer and is used as a base pointer when calling functions. It points to the beginning of the current function's stack frame. Interestingly enough, its use is actually gratuitous because compilers can manage the stack frames of functions equally well without a separate base pointer. It is mostly used to make assembly code more comprehensible for humans.

The instruction pointer rip (eip for 32-bit machines) points to the next instruction to be executed. It is paramount not to get confused when using a debugger, since the rip does not actually point to the instruction currently being executed.

The flag register rFlags (eFlags for 32-bit machines) is an isolated register which is automatically updated by the CPU after every instruction and is not directly accessible by programmes. Following is a table of the meaning assigned to different bits of this register. Note that only the lower 32 bits are used even on 64-bit machines.

In addition to the aforementioned registers, the x86-64 paradigm includes 16 registers, xmm[0-15], which are used for 32- and 64-bit floating-point operations. Furthermore, the same registers are used to support the Streaming SIMD Extensions (SSE) which allow for the execution of Single Instruction Multiple Data (SIMD) instructions.