Function:

POPA and POPAD pop all general purpose registers from the stack.
POPA pops 16-bit registers and POPAD pops 32-bit registers. The opcode is
the same. POPAD is POPA with an operand size prefix (66h).

If either POPA or POPAD is followed by an instruction which uses an
effective address calculation consisting of a base register and another
register other than (E)AX as an index, the contents of EAX is corrupted.

Also, if POPA or POPAD in 16-bit mode is followed by an instruction which
uses an effective address using EAX as a base or index, the CPU will hang.

The workaround is to always code a NOP after POPA as well as POPAD.




Prefetch queue, bus & cache parameters per CPU
──────────────────────────────────────────────────────────────────────────────

              NEC         NEC          sx  dx  sx  dx
           88 V20 188  86 V30 186 286 386 386 486 486 Pentium
         ┌─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─────┐
  SPQB───┼ 4 │ 4 │ 4 │ 6 │ 6 │ 6 │ 6 │16 │16 │32 │32 │32 x 2 │
 NEBIPQ──┼ 1 │ 1 │ 1 │ 2 │ 2 │ 2 │ 2 │ 2 │ 4 │16 │16 │     ? │
 MPBRMP──┼ 1 │ 1 │ 1 │ 1 │ 1 │ 1 │ 1 │ 1 │ 1 │16b│16b│    32a│
  DIQL───┼ - │ - │ - │ - │ - │ - │ 3 │ 3 │ 3 │ - │ - │     ? │
  OCSKB──┼ - │ - │ - │ - │ - │ - │ - │ - │ - │ 8 │ 8 │ 8 x 2 │
  DBSB───┼ 8 │ 8 │ 8 │16 │16 │16 │16 │16 │32 │32 │32 │    64 │
  ABSB───┼20 │20 │20 │20 │20 │20 │24 │24 │32 │32 │32 │    32 │
         └───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───────┛