Subject: BALR 12,12
Date: Mar 5 1990
A friend of mine told me about how he tried this on an old discrete
component machine. He tried it and the program merrily looped away.
Eventually he got tired of this and tried to halt the program. No luck.
During such jumps, the machine disabled interrupts. So he decided to
halt the machine. That just sent an interrupt, so it didn't work either.
He thought cutting the power, but was worried that an abrupt power-down
would cause a melt-down. Finally, he went and got one of the technicians.
He thought for a minute and asked at what location the instruction had
been loaded. Then he opened up the machine, found the logic for that
location (remember, this is a discrete component machine - you can
locate individual transistors) and shorted the collector to the
emitter with a screwdriver. This is what is known as "programming down
on the bare metal".
Date: Jan 2 1992
A few years ago, I was repairing a few spare boards on our CDC Hawk
drive. I had just spun the thing up to test it, when I touched a
certain board and heard a grinding noise from the heads.
Panic time - shut down first, ask questions later.
I spun it down, disassembled the disk area, and carefully inspected
the platters and heads... nothing. This was kind of curious. Well,
I reassembled it, spun it up again, and it seemed to run fine. I
then started trying to recreate the problem.
When I touched the servo controller board, the grinding noise started
again. Since I knew there was no crash, I left it going while I tried
to locate it. Then, it started to sound legible...
The heads are mounted on a coil about the size of an orange juice can,
which slides in and out of a very powerful magnet. This is also how a
speaker works. By touching a connection on the servo pre-amp, I was
acting as an antenna and picking up KQV radio, which was about 1/3
mile away from our shop. The head carriage was acting as a speaker,
somewhat hard to understand without a paper cone.
I called my boss in, who listened to it for a few seconds before he
got a huge smile on his face. He then went off to find everyone else
in our office building to show them this nifty trick.
We tried running it like this, just for kicks. Naturally, it
produced all kinds of errors. The subject was considered, but after
careful deliberation we decided not to call the radio station to
complain. Somehow, we just didn't think they'd understand.