[Simh] Simh Digest, Vol 198, Issue 16

[Johnny Billquist]

On 2020-07-10 14:19, Paul Koning wrote:
> 
> 
>> On Jul 9, 2020, at 10:40 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> On 2020-07-10 04:37, Don North wrote:
>>> On 7/9/2020 6:25 PM, Bob Supnik wrote:
>>>> Yes, the PDP11 Architecture Handbook was a post-facto effort. The J11 was finished; DEC did not intend to do another PDP11 processor. (I wrote a spec for one, primarily as an exercise in trying to do a different microcode structure than the PLA/ROM of the LSI11/F11/J11, but I lost it.) The only formal part of the PDP11 architecture was the Commercial Instruction Set extension, DEC STD 168, which was only implemented by the F11 and the 11/44.
>>> AND the PDP-11/74 CIS option, I might add. Fully implemented, never sold.
>>
>> Not to mention that the 11/74 in itself was fully implemented, but never sold... Not even the 11/70MP...
> 
> Were there actually two prototypes called 11/74?  I know the MP machine, which the RSX-11 development team owned.  And in Merrimack (home of RSTS and some of the compiler teams) there was an 11/74 with CIS, for COBOL.  But that one wasn't an MP machine.  Perhaps a coincidence, I don't have a real memory either way.

Well, yes and no...

The PDP-11/70MP is a modified KB11-C. In the end it's really just a 
modified 11/70. There are changes to the microcode, and if I remember, a 
couple of boards were changed. (See 
http://www.bitsavers.org/pdf/dec/pdp11/1174/EK-70MP-TM_PRE_1170mp_Prelim_Technical_Manual_1977.pdf).

The PDP-11/74 is the KB11-E. This was a more major redesign, which then 
allowed for the addition of CIS. (See 
http://www.bitsavers.org/pdf/dec/pdp11/1174/Prelim_KB11-E_Diffs_Aug78.pdf).

But depending on what documentation you read, they might both be called 
11/74.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol