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Tales of PDPs

A project log for Hardware assembler / EMUI

Early computer designers were cheap masochists. This front panel is much better yet could have been made 50 years ago !

yann-guidon-ygdesYann Guidon / YGDES 07/19/2018 at 01:254 Comments

Digital's minis in the 70s used a main recipe to design the front panel but there seems to be variations, even inside a given family. The main page shows the PDP8/e, but the PDP11 is interesting too :-)

This is a rebranded PDP11/70 with its red LED dots off :

(thanks to Thad for the picture ! more on Facebook )

You have to turn a knob or two to display the values you want, in raw binary. The 16-bits field on the bottom could be a register value, or the datapath, the field is unmarked so it's confusing... The 22-bits wide field just above must be a bus address, which again is not directly specified.

Notice that the rotary knob (upper right corner) has 8 positions so it could also encore octal numbers, but they decided to use only one and stick to SPST keys for data/values.

In contrast, the PDP11/20 has a more logical layout because it better matches the processor's structure:

DEC PDP-11 20 computer at the Computer History Museum (Wikipedia)

You have the address, the data, the source, the destination : it seems easier to understand at a glance what's happening.

If only they had used hexadecimal (or octal) displays instead of binary !


Oh wait, it's not LEDs ! According to Wikipedia:

"Another modification made to the PDP-10 by CompuServe engineers was the replacement of the hundreds of incandescent indicator lamps on the KI10 processor cabinet with LED lamp modules. The cost of the conversion was easily offset by the cost savings in electric consumption, the reduction of heat, and the manpower required to replace burned-out lamps. Digital followed this step all over the world."

(OK I know this is about the PDP-10 but they used similar technologies, right ?)

So my idea to use Glühbirnchen is time-accurate :-)


Meanwhile, Digital went berserk with the PDP-15:

PDP-15 control panel, restored by Mike Ross, 2012

Why did they put the key labels so far from the keys ?...


More front panel stories can be found at http://www.quadibloc.com/comp/panint.htm ! Seriously, click there, it's insane !

IBM Stretch front panel

Discussions

Julian wrote 08/20/2018 at 20:08 point

Spent a while recently digging through the various front panel layouts on the site you link (I was trying to answer this question - https://retrocomputing.stackexchange.com/questions/7262/identify-this-front-panel - although I came to the conclusion that the panel is almost certainly just a dramatic prop and not from a real computer, despite having a plausible layout and design).  It really is an amazing collection, I just wish they had more detail about what all the sections of the panels are for...

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Sophi Kravitz wrote 07/20/2018 at 13:37 point

pretty pretty

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Yann Guidon / YGDES wrote 07/20/2018 at 14:47 point

yes, it will be impossible to make something as nice-looking (yet new).

I must find other ways to shine :-D

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Artem Kashkanov wrote 07/20/2018 at 11:34 point

Oh, They are so beautiful....

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