Front panel switches - what did they do?

Swift Griggs swiftgriggs at
Tue May 24 11:32:19 CDT 2016

On Tue, 24 May 2016, Jon Elson wrote:
> 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.

How long did it usually take to do it?

> And, whenever a program crashed, it generally wiped the entire contents 
> of memory, so the boot had to be reloaded by hand. 

Uhh, ouch! That'll learn ya! You'd better be a careful coder, then I 
guess. Sheesh.

> So, that was a big advance, a one-button boot.

Man, it seems so elementary now. Everything had to be invented sometime, I 

> You could use the switches to patch a program you were debugging, look 
> at memory locations to examine temporary data values, etc.

It seems like that'd make working with computers a lot more "intentional" 
if you know what I mean. 

> A few machines had lighted switches.  These would generally be white 
> buttons with lamps behind them.

Hmm, so not as cool as 60's and 70's TV and movies seemed to suggest. 
Still at least it did happen.  :-)

> The only one I know of that changed color was the power button ("key" in 
> IBM-speak) on IBM 360's. 

Heh, my grandmother was a Cobol programmer on IBM 360s for Western 
National Gas (now Diamond Shamrock). She had mixed feelings about them, 
but she said they had a decent development environment vis-a-vis some of 
the competition at the time.

> 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.

Hmm, yeah, I seem to remember some similar style lights on old TEAC 
reel-to-reel audio gear from that era, too.

> 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.

Those multi-position switches are really cool. They remind me more of 
avionics style controls (which always seem to be the nicest physical gear 
in terms of build quality). 


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