[HECnet] Tops-20 ANONYMOUS FAL Preliminary Testing Results/DAP Query

[Johnny Billquist]

On 2019-12-21 05:21, Thomas DeBellis wrote:
> Indeed; but there was a time when the PDP-11's 16 bit (64K) address 
> space and eight register file seemed positively generous. That's when 
> you compare it to the PDP-8's /single/ accumulator and 12 bit (4K) 
> address space.

Yeah. Coming from a PDP-8, the PDP-11 is like a whole different world.

> I continue to be astounded what they managed to do with that.  In 
> addition to a nice package of languages, with a memory management unit 
> (essentially a bank switcher), they got the thing to timeshare.  That's 
> right; TSS-8.  There's one still running at the Computer History Museum 
> on an 8/I.

There are actually multiple timesharing systems for the PDP-8. I think 
Multos is way cooler than TSS-8. With Multos you get a bunch of users, 
each running their own instance of OS/8, everyone with 32K of virtual 
memory, and then a bunch of additional functions provided by the OS for 
things like communication between users and programs, getting various 
system information, spooling and what not. All with a standard omnibus 
PDP-8. No extra hardware required. And it then obviously goes beyond 
bank-switching. You actually have virtual memory, memory protection, it 
pages memory in and out as needed, and actually reduce the memory needed 
in individual users memory space, since all device drivers are already 
resident, but not in your address space. Not to mention that it can even 
make some operations be more efficient, like I/O actually being properly 
interrupt driven.

And of course, then you have things like ETOS-8, which requires special 
hardware, but also gives timesharing.

The amount of stuff possible on the PDP-8 is nothing short of amazing.

> So they got DECnet running on the PDP-8?  Wow.  I wonder how they did 
> that; whether they re-targeted a BLISS compiler to emit PAL.  I remember 
> looking at the source to PDP-8 VT (video) TECO.  Many awe most inspiring 
> kludges.  What a tour de force. Very humbling.

No BLISS for the PDP-8. DECnet-8 is written in PAL-8. And it's a set of 
services and a task or two running under RTS-8. RTS-8 is a realtime OS. 
Not too different in many concepts to RT-11 or RSX. But it's statically 
built. So you have all the tasks you might want to run compiled into one 
big binary along with the RTS-8 kernel (and DECnet-8 if you want it), 
and then you run that binary from OS/8.

OS/8 can also exist as a background task of RTS-8, so you can sortof 
continue doing development work while RTS-8 is running.

TECO-8 is very impressive. I wrote an Emacs clone in it which was rather 
decent and very usable. I believe there is a comment in there that if 
someone can just shake out a couple of more words, reverse searching 
could be implemented. That tells you how tight everything is. :-)

> The Algol compiler on the 20 has more than 2 bugs...  Sigh...

I know I've seen some Algol thingy for the PDP-8 as well, but I've never 
tested it.

   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