The Don Maslin Software Archive

[Al Kossow]

 > Since I don't beleive in using
 > old systems for the recovery of old data,

Why?

(I feel the opposite, as what better system to get the data than the 
system it
was designed for?  I'd like to hear your opinion.)

--

Almost all of the data that I recover is done at the physical media 
level. This is done either with analog to digital converters or modern
digital data separators which have better recovery characteristics than
the originals. The main reason for wanting to do this is to preserve all
of the original bit streams and error checking information.

In the case of magentic tape, it is possible to recover data from very
old tapes using modern magnetorestrictive head technology that would be
impossible to recover using the original heads, since MR heads require
MUCH less contact pressure and are much more sensitive than the originals.

While it may be practical to maintain microcomputers for this purpose
for newer media, the types of data I have been trying to recover 
(mainframes and older minis) is impractical, either because the machines
no longer exist, cannot be kept running given the tradeoff of machine
ontime vs the time needed to keep it running, or that the reliablity of 
the data from older controllers is worse than can be obtained from 
direct low-level data aquisition.

There is also the problem of file transation and transfer even if you 
can get the bits read on the original system.

The problem with using these techniques is it requires detailed 
knowledge of how the data was written and information on things like
file formats. This is why there is a strong bias towards this sort of
information on bitsavers (in addition to the fact that I've discovered
this information is REALLY hard to find for pre-minicomputer systems).

This is also information that is VERY useful to people trying to write
simulators.