Front panel switches - what did they do?

jwsmobile jws at
Tue May 24 13:00:55 CDT 2016

On 5/24/2016 9:56 AM, Swift Griggs wrote:
> On Tue, 24 May 2016, Jon Elson wrote:
>> The early PDP-11s had a diode matrix ROM for the boot memory.  You could
>> change the boot code with a wire cutter and soldering iron.
> Is that similar to "wire wrap" ? I remember my grandmother talking about
> having to snip wires connected to diodes. I think this was in the 50's but
> it might have been the 60's, too. She mentioned something like that.
Diode boards were one form of read only storage in systems.  Another was 
the IBM and other's capacitance system.

The diode boards could be done by populating a board with all possible 
diodes, then clipping them, but the cost of diodes in early days made it 
such that they typically soldered the pins into boards to create the ROM 

This is a system which used it, the Microdata 800.  This manual 
describes the assembler, and the assembler addressed the diode map as 
well as the parts map.

> -Swift

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