Originally Posted By R. Belmont
Regarding A24, it's important to note that the 68000 doesn't have a physical A0 line. There are A23-A1 and then two signals indicating which byte lane(s) are valid, so the address space is technically 0x800000 16-bit words rather than 0x1000000 (24^1) 8-bit bytes.

Interestingly, the address output buffer (the register that's routed to the address pins) has all 32 bits, and there are 24 address pads (die positions the pins are soldered to), a1-a23 and a31. The a31 pad has no pin soldered to it though.