PDP 8 Timesharing

Rick Bensene rickb at bensene.com
Mon Nov 30 12:26:08 CST 2015

Hi, all,

Just figured I'd post something about my tinkering yesterday.

I got an M8830 from Paul Anderson.  This is the crystal-contolled clock
for the Omnibus PDP 8 machines.
Yesterday, I had a chance to try it out.

First, I checked the power supply pins to make sure no shorts or
anything like that and all was good.
A quick visual inspection showed no obvious issues.
It was already jumpered for a 50Hz interrupt rate, so I went ahead and
plugged it into the backplane.  
Powered the 8/e system up, and ran a few tests from the front panel to
make sure the board was responding to its IOTs, and all seemed well.  

Booted up OS8 from RK05, and mounted up the multos8.rk05 drive via the
serialdisk driver.
Copied the MULTOS8  .SV files onto my SYS: volume, and although not
configured exactly for my system, I figured they'd be close enough.    

I then stopped the serial disk server, and fired up Kermit on the laptop
connected to the second serial port on the 8/e.  Then, I typed R MULTOS
on the console, and it said something to the effect that I needed to set
the date first.  
I generally don't bother setting the date at boot time, so I set the
date to a valid date, and tried again.  

This time it gave a welcome message. 
I checked the accumulator, and it was counting off time as it should.  I
checked the MQ register, and it was static, but then waited for the
accumulator to overflow, and then the MQ incremented by 1, as it should.

 I pressed CONTROL-H on the console terminal and hit RETURN, and there
was the . OS8 prompt!
I went to the laptop connected to the other serial interface, and since
there was no MULTOS 8 password file on the SYS: device, typed CONTROL-H
there, got the login prompt, hit RETURN, and low and behold, another .

I played around with it for a while, and found that because of some of
the config differences in how MULTOS8 was built on the pack image, some
things were acting strange but in general, it definitely was timesharing
between the two users.  
I could run concurrent things on both terminals, and the response was
quite acceptable.

I intend to make a build of MULTOS 8 to match my system's configuration,
and tinker with it some more when I get time.

Next I want to replicate the ETOS Timeshare Board (thanks to Vince and
Jack for reverse-engineering the board and making a nice schematic!)
I'm accumulating parts to build one on an Omnibus prototype board.
Once I get that built, then it'll be time to try out ETOS, which uses
the improvements in trapping IOTs and dealing with field change
instructions that really improve timesharing performance over MULTOS 8.

I am also in the process of getting ready to image some old RK05 packs
that belong to Paul Anderson that may hold some interesting ETOS stuff.
The packs have been sitting around for quite a long time, and the
platters are very dusty.   They are going to require some good cleaning
before they can be put in a drive, but hopefully, once I get them
cleaned up, I'll find some good things relating to ETOS.

I'll post updates here with my progress.

Rick Bensene
The Old Calculator Museum

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