Front panel switches - what did they do?
elson at pico-systems.com
Tue May 24 11:09:35 CDT 2016
On 05/24/2016 10:38 AM, Swift Griggs wrote:
> Since I'm an igmo about most machines before the mid-eighties (and still
> fuzzy even on most of those), I'm curious about all these older machines
> with front panel buttons and switches. What all did they do? You could
> actually program them using the front panel right? Some of them
> bootstrapped this way, too? What kind of "language" was used for that
> (ie.. what were the basic mechanics)? Did the buttons ever change color?
> Were you considered a badass if you had switch flipping all memorized down
> to an art? Were they mainly multi-position toggle switches or on/off
The PDP-5 I did a fair bit of work on needed a bootstrap
program loaded in from switches, it had no internal ROM for
that. And, whenever a program crashed, it generally wiped
the entire contents of memory, so the boot had to be
reloaded by hand. We actually wore out the switches. It
was about 15-20 12-bit words that needed to be entered. We
had DECtape on that machine, so we generally entered to boot
loader for that.
The LINC was also a 12-bit computer, but it had built-in
boot hardware. it was not a boot loader program in a ROM,
but when you pressed the load button, it would execute an
I/O command from the left switches, and the right switches
told it where to put it in memory. So, that was a big
advance, a one-button boot.
You could use the switches to patch a program you were
debugging, look at memory locations to examine temporary
data values, etc.
A few machines had lighted switches. These would generally
be white buttons with lamps behind them.
The only one I know of that changed color was the power
button ("key" in IBM-speak) on IBM 360's. It lit red while
the power-up sequence was in progress, then turned white
when all power supplies were up. IBM tape drives and disk
drives had lighted buttons to show status, different color
buttons and indicators gave them different colors, but they
were generally just lit and unlit, but not multi-color.
DEC PDP machines generally had a few switches that were
multi-position, Such as stop/single-step and load
address/examine, otherwise they were all on-off.
IBM 360's had a row of switches that were multi-position,
mostly for FE diagnostic purposes. The data and address
switches were all on/off.
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