Grand Central provides support for eleven system interrupts. On both the Macintosh and the ANS, each PCI slot contains only one interrupt line (up to four supported in PCI spec.) and each interrupt line is used by only one device. The interrupt map is different in the two machines, and this represents the most likely reason why inserting a PM9500 or PM9600 ROM in an ANS will not allow the machine to boot. The firmware expects certain interrupts to correspond to certain events, but the interrupt signal is physically connected to a different device than the firmware expects.