John Payson wrote:

> The only time a ROM checksum routine is really useful is if
> the checksum routine itself is stored in a more reliable
> medium than the code being checked.

I agree with part of the comment however the real role of a
checksum routine is to prevent in-operative code from
executing.  Careful design of the checksum routine can
result in the failure modes of the checksum preventing the
application from running. In critical systems the checksum
routine which is quite small becomes the focus of very careful
anaylsis.

Walter Banks