31 Oct
2024
31 Oct
'24
9:16 p.m.
remember, core memory is destructive read out. to read the bits you erase them and have
to rewrite them.
I doubt the B * running for 30 seconds, then cancel the job would be bad, but if you
started it up Friday and it ran all weekend? every time you demagnetize and re-magnetize
those cores, probably an atom
or two gets displaced.
<pre>--Carey</pre>
On 10/31/2024 7:02 PM CDT Jon Elson via cctalk
<cctalk(a)classiccmp.org> wrote:
On 10/31/24 09:35, Donald Whittemore via cctalk wrote:
If I remember right I was told back in the early
70s by our IBM CE that physical damage could be done to our model 30 or 40 if we ran a
program that did an Assembler instruction, B * For those non-Assembler people that is
an instruction to branch to the location of the instruction. I think it might have caused
a heat problem in the core or CCROS or TROS.
Possible? Or is my 76 year old brain hallucinating?
Hammering a single location in core could overheat the
select wires, the individual cores or the select driver
cards. I can believe this could happen. I seriously doubt
it could harm the CCROS or TROS. The model 30 was SLOW, the
original version (first 1000 machines) had a 2.5 us memory
cycle time. But, a B instruction occupied 4 bytes. And the
model 30 memory was ONE SINGLE BYTE wide! So, it would have
to access 4 consecutive bytes over a 10 us period to read
the entire instruction. This would involve t different
select wires in one axis, but likely the same wire in the
other axis.
On the model 40, memory was 16 bits wide, so it would still
have to access 2 consecutive words.
Anyway, I was told that on a model 40 (I think) that if you
pressed and held stop, system reset, and load
simultaneously, it would pop a component on a circuit card
in the machine.
Jon