Reproducing old machines with newer technology

Paul Koning paulkoning at
Wed Jul 15 09:16:16 CDT 2015

> On Jul 14, 2015, at 11:36 PM, Chuck Guzis <cclist at> wrote:
> On 07/14/2015 07:11 PM, William Donzelli wrote:
>>> I suppose you could view it that way.  There were CPU-less 6000 boxes, but
>>> no PPU-less ones.
>> Were the CPU-less 6000 boxes at least connected to "normal" 6000s with
>> CPUs using shared ECS, or could they really be completely independent
>> units using their own ECS?
> The 6416 was a special beast--I don't know that CDC ever produced any standard software for it. It had 16KW of CM and it's own ECS coupler, so I suppose that it could share ECS with other machines--but IIRC the ECS access was via its own special instructions.

I just found it, in the old (rev B) version of the System Programmer’s Instant.  It’s the 6411/6414 “Augmented I/O Buffer and Controller”.  And yes, it has its own ECS instructions, which use what would normally be NOP opcodes.  Interesting, given that conventional PPUs got ECS access via the DDP, an I/O device.  I suppose they wanted to integrate it a bit better, or use less logic?
> I suspect that some 6416s just communicated with other systems using the 6682(?) satellite coupler.  I suspect that they were largely superseded by the "additional PPU" machines.
> I never ran into a 6416 in the flesh, but was aware of more than one 20 PPU 6000 (there were never enough PPUs).  CDC also offered "PPU-reduced" models of the 6400,  with up to 3 PPUs removed, which never made any sense to me.

Same here.  The PLATO system was pretty demanding of PPUs, but still it managed with the standard 10.  Partly that may be because it didn’t really use the standard CDC ones at all, relying on its own dedicated ones instead.  One for terminal I/O, two for disk I/O, one for OS-like functions — four persistent ones, that still leaves another four “pool” PPs.


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