specially-packaged 286 system with 256MB RAM and 256MB ROM, and
I'm guessing
you meant to say "256KB RAM and 256KB ROM"; otherwise, that
computer would've probably cost several times more than the car in which
it was used--at least back in the mid-1980s.
Plus, the regular models of the 286 had 24 address lines, and therefore,
anything more than 16M would have required some sort of bank-switching.