Andy Ball wrote in a message to Roy J. Tellason:

 AB> Hello Roy,

  RJT> OTOH,  since the first one that I was exposed to was a PDP-11
     > /03 (aka Heathkit H11) I thought that 8 16-bit registers was
     > about right.

 AB> What I've read about the PDP-11 gives me the impression that it's 
 AB> well thought-out design that could be enjoyable to program.

The feeling I got from what I could see of things tends to confirm this. 
Unfortunately there were a lot of conventions,  assumptions,  and other
bits that I never did get back in those days,  which kind of limited my
ability to do much with it.

 AB> If a small -11 (and /03 would be about perfect) comes along I may 
 AB> pick one up.  There are plenty of emulators around too.

The biggest problem I have with this idea is that the hardware is very
different from anything else out there,  and finding any sort of boards to
plug into it would be difficult.

The machine used an asynchronous bus,  sort of like what the 68000 does, 
and I tried to build a board to fit into it.  This was for i/o,  I wanted
to interface a dual cassette deck to it that was commercially available at
that time and *way* cheaper than any of the DEC stuff.  I couldn't get the
machine to talk to the board at all.

Then,  with the /03 at least,  you're limited to 56k ("words") of
ram in the box.  Which didn't stop such things as MU-BASIC,  supposedly
able to support up to 8 users at once,  but we couldn't get that working
either.  It was more a matter of not having the appropriate multiple
terminals and storage options installed,  I think.

  RJT> And the "extra" stuff that the z80 gave you was such a kludge,
     > sort of just tacked on to one side, as if maintaining
     > compatibility with the earlier parts was such an important
     > issue.  Maybe it was,  I dunno.

 AB> CP/M-80 was the industry standard operating system of the day.

It sure was.  But then there were a bunch of interesting variants on it
too.  Things like MMMost,  TurboDOS,  and a few others,  that added
capabilities.  I never did mess with MP/M,  either,  but from what I
understand that was pretty crude.

 AB> The Z80's backwards compatibility enabled it to run that and 
 AB> eventually CP/M 3 (a.k.a. CPM+) was released and as I understand 
 AB> it, depends on features of the Z80.

Not that I'm aware of.  I ran an Osborne Executive for years after
everybody else had gone to clone hardware,  and in fact the major reason I
eventually made the change was fidonet -- I wanted to run point software, 
and there was no way I could get the one cp/m point package to work.  The
Exec did have a z80 in it,  to be sure,  but nothing in the OS actually
depended on it being there.  In fact,  the original 1.2 rom code for that
machine used the alternate register set for handling keyboard interrupts! 
That broke a few programs that did need a z80 and those registers,  most
notably Turbo Pascal and Mix C.  I ran a "TPATCH" program as a
part of my boot process before I ended up replacing the eprom with a 1.21
version that I'd burned.

 RJT> To me, the 65xx and 68xx parts always seemed "weird".  :-)

 AB> They're an acquired taste ;-)

Yeah,  I guess.  I did get together with some friends and we got these
books on 64/128 assembly language,  and got together and studied it for a
while.  And I got copies of the assembler,  etc. that everybody was using, 
but I never actually did anything with it. 

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