1. 2
  1.  

  2. 1

    (My nitpick: the VIA C3 “privileged coprocessor” with an “undocumented” instruction is neither - the instruction to do so is documented, as is the mode it enabled, “altinst”, which effectively is CPU µcode. What was undocumented (unless you didn’t mind signing an NDA to get access to it) was the µcode ISA documentation.