In A500, the address decoding performed by the Gary chip could be disabled with the /OVR override signal, for certain address spaces only, but not the area which used by this hack. But it seems to be work in practice. In the Commodore Amiga A500/A2000 Techical Reference Manual, on the 86-pin connector, page 93: " The /OVR, override, signal is a special Amiga expansion signal that can serve two purposes. The signal can basically turn off the on- board decoding of system memory ranges. As a result of this, it can also turn off internally generated things, like /DTACK. The timing in the A500 and B2000, based on the Gary chip (not the PALs of the older machines) effectively prohibits the use of OVR* for the area outside of $200000 and $9FFFFF. " ... it continues to say that the use of this signal for tristating the /DTACK is better supported. "The other use of this signal is better supported. Asserting /OVR will tri-state the internally generated /DTACK signal, allowing a Co- processor or Expansion device to create its own /DTACK, The same effect can be achieved for most applications by using XRDY to delay the motherboard's generation of /DTACK. Pin 17." NOTE: On 100-pin Zorro Slot the timings could be much less supportive of this use.