[TUHS] Software written in B

Phil Budne phil at ultimate.com
Thu Jun 8 04:16:55 AEST 2023

Here's what I know about surviving early UNIX B implementations bits:

Two surviving B programs from PDP-7 UNIX listings:

NOT a b program, but for "fun" I tried my hand at recreating the TMG
compiler compiler for the PDP-7 (we only have the original library
routines, but not the TMG (.t) source for the compiler at:

https://github.com/philbudne/pdp7-unix/tree/tmg/src/other/pbtmg and
tried writing a B compiler in TMG (b.t in the above directory) based
on Robert Swierczek's decoding of the B interpreter/runtime.

Both the PDP-7 and (initial?) PDP-11 B compilers generated interpreted code.

I'm not aware if the PDP-11 B compiler source has ever been unearthed,
but a ar(chive) file of the library and interpreted was found, and
Robert S posted disassemblies here:


With this explanation of where the files were discovered:

As well as

Which I added to Robert's tree in a private branch that I guess
I never opened a Pull Request for:

And I (think) I had to make up brt1.s and brt2.s files:

based on the usage description in Ken's manual:
https://www.bell-labs.com/usr/dmr/www/kbman.html :
	ld object /etc/brt1 -lb /etc/bilib /etc/brt2

I tried to hack Robert's PDP-7 B compiler to work with the above
PDP-11 runtime:

But I don't remember what state I left it in.

Ken's manual indicates that the original PDP-11 B compiler had two
phases: "bc" which generated intermediate code, and "ba" which turned
that into a .s file.

A "fun fact" about all the above compilers (TMG and B) for both the
PDP-7 and the PDP-11 is that the compilers (eventually) output
assembly language source that was assembled (and for the PDP-11
loaded) with an interpreter library and runtime.

I seem to recall that for the PDP-7, the interpreted code (for both
TMG and B) looks much like PDP-7 instructions (same number of high
order "opcode" bits, some use of the indirect bit, and an address
field while the PDP-11 B compiler (at least) generated code is more
like threaded code, with an interpreter program counter in r3, and
"jmp *(r3)+" to dispatch to the next instruction.

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