[TUHS] b remnants?

[gregg.drwho8@gmail.com (Gregg Levine)]

On Sat, Oct 15, 2011 at 12:20 AM, Jason Stevens
<jsteve at superglobalmegacorp.com> wrote:
> Wasn't the other 'advantage' of threaded/pcode that it'd be smaller than a
> native executable?
>
> I know it's out of left field, but building Dungeon on RT-11, you have to
> use the treaded compiler, and I assume it was a space thing.. Just as on
> MS-DOS (Yeah I know...) a save for fitting stuff in 64kb for the later
> compilers was to compile to p-code..
>
> Wikipedia gives p-code for Pascal a timeframe of the 'early 70's and
> attribes the whole interpeted code as O-Code for BCPL ....
>
> I wonder if anyone ever did save any TripOS tapes for the PDP-11.....
>
> -----Original Message-----
> From: A. P. Garcia [mailto:a.phillip.garcia at gmail.com]
> Sent: Friday, October 14, 2011 11:58 PM
> To: tuhs at minnie.tuhs.org
> Subject: Re: [TUHS] b remnants?
>
>
> On Fri, Oct 14, 2011 at 9:52 AM, A. P. Garcia
> <a.phillip.garcia at gmail.com> wrote:
>>
>> In memoriam, I read The Development of the C Language:
>> http://cm.bell-labs.com/who/dmr/chist.html
>>
>> It talks a bit about how B was originally implemented somewhat like
>> ETH Pascal (p-code). Are there any B interpreters or programs in the
>> archive?
>
> What intrigued me about this is that it's such an early example of an
> abstract machine running as an interpreter. BCPL, roughly
> contemporaneous, used ocode as an intermediate language, but it seems
> this was intended to be further translated into assembly. While it's
> possible to interpret ocode, in practice it seems this was rare, if it
> was done at all. Almost everything I've read about abstract/vitual
> machines traces its roots back to the following source:
>
> James R. Bell. 1973. Threaded code. Commun. ACM 16, 6 (June 1973),
> 370-372. DOI=10.1145/362248.362270
> http://doi.acm.org/10.1145/362248.362270
>
> Here's where dmr mentions implementing B using this technique:
>
> The B compiler on the PDP-7 did not generate machine instructions, but
> instead `threaded code' [Bell 72], an interpretive scheme in which the
> compiler's output consists of a sequence of addresses of code
> fragments that perform the elementary operations. The operations
> typically-in particular for B-act on a simple stack machine.
>
> Note he says it was published in 1972, when it actually appeared in
> print in 1973 (same page numbers). Two paragraphs later he writes:
>
> By 1970, the Unix project had shown enough promise that we were able
> to acquire the new DEC PDP-11. The processor was among the first of
> its line delivered by DEC, and three months passed before its disk
> arrived. Making B programs run on it using the threaded technique
> required only writing the code fragments for the operators, and a
> simple assembler which I coded in B; ; soon, dc became the first
> interesting program to be tested, before any operating system, on our
> PDP-11. Almost as rapidly, still waiting for the disk, Thompson
> recoded the Unix kernel and some basic commands in PDP-11 assembly
> language. Of the 24K bytes of memory on the machine, the earliest
> PDP-11 Unix system used 12K bytes for the operating system, a tiny
> space for user programs, and the remainder as a RAM disk. This version
> was only for testing, not for real work; the machine marked time by
> enumerating closed knight's tours on chess boards of various sizes.
> Once its disk appeared, we quickly migrated to it after
> transliterating assembly-language commands to the PDP-11 dialect, and
> porting those already in B.
>
> The abstract machine is also mentioned in Thompson's "Users' Reference
> to B", dated January 7, 1972. If the 1970 date is correct, they were
> using this technique some three years before most of the computing
> world knew about it!?

Hello!
This discussion is beginning to strike a heck of a lot of chords.
Jason what is this TripOS you are describing here about? And did you
actually get Dungeon to work?

-----
Gregg C Levine gregg.drwho8 at gmail.com
"This signature fought the Time Wars, time and again."