[Simh] pdp7/decsys bug?

[Daniel Baum]

> Daniel wrote:
>> I have had several successes (I will list them if anyone's interested), 
>> but
>> I believe it is possible that there is a bug in the pdp7 simulator.
>
> Sorry I can't help you track down the bug, but I think it'd be great if 
> you posted your successes!

Hi,

Well, since you asked . . .  Here is what I have made work, with some 
impressions.

I originally installed simh to get a look at the early unixes, and the early 
C compilers so:

UNIX V5 (PDP-11) - surprisingly like a rather simple-minded Linux. 
Everything seems to work. It has a primordial C compiler, pre-Kernighan & 
Ritchie. The distribution comes with loads of source code and I had no 
trouble compiling it. There is also a Fortran IV compiler, called fc, which 
I got to work, once I had worked out what kind of file format it wanted. It 
also has a totally bizarre Basic interpreter, which works OK, but has really 
odd syntax, like "for I=1 10".

UNIX V7 (Interdata) - The PDP-11 version of Unix V7 doesn't work as well as 
the Interdata version, so this is the one I used. It has THE K&R compiler. 
(K&R actually gives specs for the Interdata version) It also has a Fortran 
77 compiler, which is supposed to be the earliest one in existence. It works 
OK. I originally had a problem in that it wouldn't compile any file with 
real variables, but it turned out that it required double precision fp 
support in the CPU. Could this be a clue as to the PDP-7 problem? Overall, a 
much fuller system than V5 and much more like modern Unix, except for the 
apparent lack of networking . . . hmmmm, Unix without networking. . . .

Once I'd taken a look at these, I decided to widen my horizons with some 
other systems.

TSS/8 (PDP-8)  - a tiny multi-user system. Quite likeable. I managed to 
write programs in Basic and Algol, but had no success whatsoever with 
Fortran. Nothing compiles, including demo programs, leading me to assume 
that there is a file missing or something. I also managed to assemble a demo 
program with the assembler, but I think assembler is rather beyond the call 
of duty.

OS/8 (PDP-8) - a much more polished, and apparently much less ancient system 
than TSS/8. It has Fortran IV, which works well , as well as Basic. These 
old Basics are very nostalgic. My first home computer has Basic like this. 
The text editor is quite similar to that of TSS/8, but has evolved somewhat 
to make it (a bit) easier to use.

DecSys (PDP-7) - Primaeval. A bit like driving a Model-T Ford -  full of 
historical interest, but not something you'd want to do every day. It is, in 
fact, almost ludicrously awful to use.  Was this considered usable in 1966? 
It's no wonder they wrote Unix for this machine, if this was the 
alternative. It has Fortran II, which, as mentioned, for some reason I can't 
get to handle floating point values properly, and assembler, which 
apparently works because it is part of the Fortran compilation chain. The 
text editor is feeble, and, like the rest of the system inconsistent, 
unfriendly and quirky. Don't expect luxuries like the ability to delete 
files, and NEVER press the wrong key; or you might end up with two files 
with the same name . . .

It's all been great fun, and very interesting.

Daniel