2. Mirage Microdrive .SNA format used by Spectrum 1.7 and JPP
   Notice, that in Intel CPUs the least significant byte goes first.
   When the registers have been loaded, a RETN command is required to
   start the program. IFF2 is short for interrupt flip-flop 2, and for
   all practical purposes is the interrupt-enabled flag. Set means
   enabled.

Offset   Size   Description
------------------------------------------------------------------------
0        1      db    I
1        8      dw    HL',DE',BC',AF'
9        10     dw    HL,DE,BC,IY,IX
19       1      db    Interrupt (bit 2 contains IFF2, 1=EI/0=DI)
20       1      db    R
21       4      dw    AF,SP
25       1      db    IntMode (0=IM0/1=IM1/2=IM2)
26       1      db    BorderColor (0..7, not used by Spectrum 1.7)
27       49152  RAM dump 16384..65535
------------------------------------------------------------------------
Total: 49179 bytes