11 Nov
2008
11 Nov
'08
12:56 p.m.
On 10 Nov 2008 at 16:05, Eric Smith wrote:
At least in the case of the HP9100, I am pretty sure it was tested
_electrically_. One of the HP journals mentions some spcial-purpose test
rigs used at the factory that compared the core-on-a-rope microcode store
and the PCB main store with known-working examples.
That said, there is a (temporarily) destructive visual method that would
work on the HP9100 microcode sotre, I think. Namely to desolder each
address wire from the PCB at one end (HP were kind enough to label the
endpoints of these wires, so you can note down half the address at this
point), then carefully untrhead it from the cores, ntoign which cores it
loops through, and finally note down the other hald of the address from
where it conencts to. Do that for all 64 wires and you have a 'dump' of
the ROM. Finally, of course, replace and re-thread all the wires to
restore the ROM contents.
-tony
Not really. You'd have thousands of very
fine wires, all looking
identical, that pass through some cores and go around others (on average
perhaps 33 through each core), and packed incredibly densely. Even with
very high resolution scans from multiple angles I don't think you could
expect to extract the data visually.
Okay, I see. Regardless--if it's that type of memory, then failure
to read it electrically could use a visual method as a fallback.
After all, these things were assembled (and one would expect,
inspected) manually.