Disk archival techniques

[Tony Duell]

 > As a matter of fact, I just dumped several Cromemco PROMs a while ago 
> for archival use;
> what's the recommendation for 4 bit PROMs? 8 bits with hex F's in the 
> upper nibble, or? 

I normally use 8 bits per location, data in the low bits, top 4 bits
don't-cares (eitehr 0 or F is common), but all the same for a given dump. 
Anybody seeing that in the future who knows that it's a dump of a 4-bit
wide device will soon realise that as the top 4 bits of each byte are 
constant, it's likely that the useful data is the bottom 4 bits only.

> 
> And are we going to be able to find blank bipolar PROMS or PALs in 10 
> or 20 years? 

Prbably not, but there _will_ be fast-enough memory devices that can be 
programmed and kludged into the board in place of the failed part. The 
fact that you might only be using the bottom 32 bytes of an 8Mbyte part 
won;t be a worry I guess.

-tony