70's computers

[Jon Elson]

On 10/25/2018 02:24 PM, allison via cctalk wrote:
> Likely make a fortune off my stockpile of 2901s. Building 
> machine from the earth up is not that hard, software to 
> make them useful is a big deal.
Yes, and that's where my 32-bit 2903 project started to bog 
down.  I knew some people, OS security was a total joke, so 
I COULD have just stolen OS 360 MVT, but REALLY, who would 
do that to themselves?
I had a few more bits of logic to wire in, to make a 256-way 
branch from the OP-code field of the instruction register to 
decode instructions, and from the register fields of the 
instruction register to OR into the register address.  Then, 
I had to write the microcode.  I'd done some small test bits 
of microcode, including the multiply, and that worked.  
(IIRC, the 2903 has an extra shift register, so it can do 
the multiply step in one CPU cycle, the 2901 takes 2.)

Well, after that, I had a big decision to make.  Should the 
memory be on the system bus, like PDP-11 and VAX, or part of 
the CPU, like IBM-360 and PDP-10?  Then, I had to get memory 
wired to the bit slice system, and then build peripheral 
controllers.  I had a very rough concept scratched up, about 
30 chips to make a microcoded 16-bit machine, using fast 
EPROMS for the control store.  A SCSI interface would be 
pretty trivial, but a read-after-write mag tape control and 
an 8-channel serial multiplexer would be much more 
complicated project.  THEN, the big stuff would come, I'd 
need an OS and language compilers.  I could probably whip up 
a version of CP/M with hierarchical directories and 
time/date stamps, and maybe a simple editor, but the WHOLE 
REASON for this project was to move up to modern high-level 
languages.  And, I had badly underestimated how difficult 
that might become.  One scheme might be to start with my 
CP/M-like OS, and build a wrapper program that would allow 
me to run OS-360 compilers and linkers with whatever object 
libraries they needed, and then use them to compile 
something more to my liking like Pascal.   But, it was all 
looking like a LOT of work.

So, I managed to clone a Nat. Semi 32016 system and got it 
running, but it was amazingly slow.
I suspect that my kluged memory interface was not fully 
optimal, but even the original that I copied was pretty 
slow.  Then, I spent BIG BUCKS to buy a uVAX-II CPU board 
from a broker, and was finally in HOG HEAVEN!  It was 
certainly fast, almost the speed of the VAX-780's I used at 
work, and ALL MINE!

So, that's my story.

Jon