Search code examples
assemblyx86x86-64intelmachine-code

What does 'REX' stand for in an x86-64 REX prefix?

From Intel's SDM, section 2.2.1 specifies that the REX prefix is used to:

  • Specify GPRs and SSE registers.
  • Specify 64-bit operand size.
  • Specify extended control registers

But what do the letters REX stand for in the acronym?

Solution

  • This 2002 Hot Chips presentation by AMD expands the acronym on slide 10: "REX (Register Extension)".

    Kevin McGrath and Dave Christie, "The AMD x86-64 Architecture: Extending the x86 to 64 bits", Hot Chips 14, August 2002.