Thinking about acquiring PDP stuff

Brad H vintagecomputer at
Thu Dec 1 00:01:01 CST 2016

-----Original Message-----
From: cctalk [mailto:cctalk-bounces at] On Behalf Of Rich
Sent: Wednesday, November 30, 2016 12:16 PM
To: 'General Discussion: On-Topic and Off-Topic Posts'
<cctalk at>
Subject: RE: Thinking about acquiring PDP stuff

From: Brad H
Sent: Wednesday, November 30, 2016 9:16 AM

> That was kind of why I thought buying a PDP in pieces over time might 
> be my way to go, even if it took eons to get everything I needed to
rebuild one.
> It'd be fun to try and piece one back together.  But yeah, I'm trying 
> to think of what I would do with it afterwards. :)

So what kind of system are you interested in?  There is no such thing as a
generic "PDP".  Before giving up the naming convention, DEC produced 7
different architectures all named "PDP-n" for small integers n (and designed
2 that were never built by DEC):

PDP-1:  18 bits, 6 instruction + 12 address (System Modules)
PDP-2:  24 bits (design only) (System Modules)
PDP-3:  36 bits (design only) (System Modules)
PDP-4:  18 bits, 5 instruction + 13 address (System Modules)
PDP-5:  12 bits (System Modules)
PDP-6:  36 bits, 9 instruction, 9 AC+index+indirect, 18 address (mainframe)
PDP-7:  18 bits (PDP-4 upwards compatible) (FlipChips)
PDP-8:  12 bits (PDP-5 upwards compatible) (FlipChips)
PDP-9:  18 bits (PDP-7 upwards compatible) (FlipChips)
PDP-10: 36 bits (PDP-6 upwards compatible) (mainframe)
PDP-11: 16 bits (FlipChips)
PDP-12: 12 bits (PDP-8 + LINC compatible) (FlipChips)
PDP-14: 12 bits (NOT compatible with the PDP-8 family) (FlipChips)
PDP-15: 18 bits (PDP-9 upwards compatible) (FlipChips)
PDP-16: register-transfer module machine, with 8-, 12- or 16-bit memory as
	needed for particular application design.

Later members of each family were designated by suffixes (e.g. 8/i, 8/e, 8/A
and 11/40, 11/70, etc.) or newer names (DECsystem-10, DECSYSTEM-20).  The
VAX was the first new architecture from DEC not to have a PDP-n designation
at all.


P. S. For most of us, I think, "DG" = Data General, not Digital Group.

Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

>mailto:RichA at


Can I use 'dg'? :)  I think Digital Group preferred to be uncapitalized if I
remember correctly.

Regarding PDP -- I'm just sort of dipping my toes in here.  I'd like
something that looks similar to an 8/E -- front panel toggle switches,
preferably from before 1975.  But it's all a function of price.. if I can
find a later 11 that isn't $600+, that might be a place to start.  I'm open
to suggestions.  I've always been curious about DEC -- the computer shop we
once frequented in Vancouver always had stacks of DEC stuff among its used
computer inventory.  VAX stations mostly.  But I never got around to buying
anything.  Was too busy collecting classic Macs.

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