What are the sizes of tword, oword and yword operands?

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Looking at the nasm source, it looks like:

  • ‘oword”https://stackoverflow.com/”DO’ is 8 times as big as “word” (O for “octoword”), synonymous with dqword (“double-quad”); that would be 128 bits, corresponding to the size of an SSE vector register.
  • ‘tword”https://stackoverflow.com/”DT’ is 80 bits (T for “ten bytes”), the full size of an Intel x87 floating point register.
  • ‘yword”https://stackoverflow.com/”DY’ is 256 bits, and the Y is presumably mnemonic for the YMM names of the 256-bit vector registers in the Intel AVX extensions.
  • ‘zword”https://stackoverflow.com/”DZ’ is 512 bits, Z for the ZMM names of the 512-bit vector registers in the Intel AVX-512 extensions.

So, it’s not exactly a logical naming convention; “it just growed”.

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