Most sideways ROM board
s for the BBC microcomputer
would let you plug in one RAM chip
instead of a ROM
. Then you could write your own ROM image
, and it would work exactly as if that ROM
was plugged in. Of course, you had to get the image somehow. While some people pirate
d ROMs, it was certainly possible to write your own image, or type it in from a magazine
like Micro User
or Acorn User
. In fact, some images had
to run from RAM, as they wrote back to the image!
Some boards would let you plug in a CMOS 62c64 (or 62c128) instead of a 6264 (or 62128), and would then keep it powered using a battery backup. This was not so good: if the ROM was corrupted in such a way as to cause the OS to recognise it on powerup, you had to take the battery out to get the computer to boot!