In 1992, 386BSD is released by Lynne and William Jolitz, starting the open
source operating system movement (Linux didn't come along under later).
-- Dave
Unlike most here, I always pronounced Mt Xinu with an
eye, not an eee. I don't know where I got that, though.
I did know Ed Gould via USENIX and DECUS, but that doesn't
make my pronunciation correct.
As an aside, anyone know where Ed is these days or how he's
doing? I last saw him at a USENIX conference, probably in
San Jose in 2013 but I'm not sure. He showed up just for the
reception; he'd retired, and had cut away most of his famous
beard because he was spending a lot of time sailing and it
got in the way.
Norman Wilson
Toronto ON
Nelson H. F. Beebe:
P.S. Jay was the first to get Steve Johnson's Portable C Compiler,
pcc, to run on the 36-bit PDP-10, and once we had pcc, we began the
move from writing utilities in Pascal and PDP-10 assembly language to
doing them in C.
======
How did that C implementation handle ASCII text on the DEC-10?
Were it a from-scratch UNIX port it might make sense to store
four eight- or nine-bit bytes to a word, but if (as I sense it
was) it was C running on TOPS-10 or TOPS-20, it would have had
to work comfortably with DEC's convention of five 7-bit characters
(plus a spare bit used by some programs as a flag).
Norman Wilson
Toronto ON
More from Yost below.
My purpose in relating this was to point out that the original unix
implementation choices were mostly fine; they just had to be tweaked a
bit. Clearly an independent implementation such as in Linux would veer
off in a different direction, done in a different era and with different prior
experience. I was a bit surprised that Bruce didn't make this same
tweak to cblock size but no way of knowing his reasons now.
> Begin forwarded message:
>
> From: Dave Yost
> Subject: Re: [TUHS] 386BSD released
> Date: July 16, 2021 at 9:21:53 AM PDT
> To: Bakul Shah
>
> Plz forward this
> thanks
>
> This was in early 1983 or late 1982.
>
> We got the serial driver to go 19200 out and 9600 in.
>
> I did 2 things in the Fortune Systems 68k serial driver:
> • hand-coded asm pseudo-DMA, suggested by Robert P Warnock III
> • cblock size 128 bytes instead of 8, count ’em, 8.
>
> From Lyons,
> https://cs3210.cc.gatech.edu/r/unix6.pdf <https://cs3210.cc.gatech.edu/r/unix6.pdf>
> the unix v6 serial driver used a clist of cblocks, like this:
>
>
> The pseudo-DMA interrupt handler was a function made up of a few hand-coded 68k instructions, entered into C code as hex data. That code transferred one byte into or out of a cblock, and at the end of the cblock it grabbed the next cblock from a queue and rang the “doorbell” hardware interrupt, which caused a “software interrupt” at lower priority for further processing. Rob put the doorbell into the architecture with a couple of gates on the board because he was well aware of this software interrupt trick, which was already used in bsd. For some reason I didn’t look at the bsd code, probably because Rob’s explanation was lucid and sufficient.
>
> I once had occasion to mention this, and specifically the relaxing of the draconian 8 byte cblock size, to Dennis Ritchie. He said, sure, why not, the 8 byte cblock size was just a neglected holdover from early days.
>
> This approach was just an interrupt version of what I had proposed to Rick Kiessig as a first project at Fortune Systems: to get a 30x speed up when writing to the Fortune Systems memory-mapped character display hardware. I had done the same thing a few years earlier in Z80 in C code in a serial CRT terminal. It’s simple and obvious: make the inner loop do as little as possible. The most primitive operation needs to be a block operation, not a byte-at-a-time operation.
Doug McIlroy asks about the Rosetta Stone table relating TOPS-20
commands to Unix command in my ``Unix for TOPS-20 Users'' document:
>> I was puzzled, though, by the Unix command "leave", which is
>> not in the manuals I edited, nor is it in Linux. What does
>> (or did) it do?
I reread that 1987 document this morning, and found a few small
mistakes, but on the whole, I still agree with what I wrote 34 years
ago, and I'm pleased that almost everything there about Unix still
applies today.
I confess that I had forgotten about the TOPS-20 ALERT command and its
Unix equivalent, leave. As Doug noted, leave is not in Linux systems,
but it still exists in the BSD world, in DragonFlyBSD, FreeBSD,
NetBSD, OpenBSD, and their many derivatives. From a bleeding-edge
FreeBSD 14 system, I find
% man leave
LEAVE(1) FreeBSD General Commands Manual LEAVE(1)
NAME
leave – remind you when you have to leave
SYNOPSIS
leave [[+]hhmm]
DESCRIPTION
The leave utility waits until the specified time, then reminds you that
you have to leave. You are reminded 5 minutes and 1 minute before the
actual time, at the time, and every minute thereafter. When you log off,
leave exits just before it would have printed the next message.
...
-------------------------------------------------------------------------------
- Nelson H. F. Beebe Tel: +1 801 581 5254 -
- University of Utah FAX: +1 801 581 4148 -
- Department of Mathematics, 110 LCB Internet e-mail: beebe(a)math.utah.edu -
- 155 S 1400 E RM 233 beebe(a)acm.org beebe(a)computer.org -
- Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ -
-------------------------------------------------------------------------------
Clem Cole asks:
>> Did you know that before PCC the 'second' C compiler was a PDP-10
>> target Alan Snyder did for his MIT Thesis?
>> [https://github.com/PDP-10/Snyder-C-compiler]
I was unaware of that compiler until sometime in the 21st Century,
long after our PDP-10 was retired on 31-Oct-1990.
The site
https://github.com/PDP-10/Snyder-C-compiler/tree/master/tops20
supplies a list of some of Snyder's files, but they don't match
anything in our TOPS-20 archives of almost 180,000 files.
I then looked into our 1980s-vintage pcc source tree and compared
it with a snapshot of the current pcc source code taken three
weeks ago. The latter has support for these architectures
aarch64 hppa m16c mips64 pdp11 sparc64
amd64 i386 m68k nova pdp7 superh
arm i86 mips pdp10 powerpc vax
and the pdp10 directory contains these files:
CVS README code.c local.c local2.c macdefs.h order.c table.c
All 5 of those *.c files are present in our TOPS-20 archives. I then
grepped those archives for familiar strings:
% find . -name '*.[ch]' | sort | \
xargs egrep -n -i 'scj|feldman|johnson|snyder|bell|at[&]t|mit|m.i.t.'
./code.c:8: * Based on Steve Johnson's pdp-11 version
./code2.c:19: * Based on Steve Johnson's pdp-11 version
./cpp.c:1678: stsym("TOPS20"); /* for compatibility with Snyder */
./local.c:4: * Based on Steve Johnson's pdp-11 version
./local2.c:4: * Based on Steve Johnson's pdp-11 version
./local2.c:209: case 'A': /* emit a label */
./match.c:2: * match.c - based on Steve Johnson's pdp11 version
./optim.c:318: * Turn 'em into regular PCONV's
./order.c:5: * Based on Steve Johnson's pdp-11 version
./pftn.c:967: * fill out previous word, to permit pointer
./pftn.c:1458: register commflag = 0; /* flag for labelled common declarations */
./pftn2.c:1011: * fill out previous word, to permit pointer
./pftn2.c:1502: register commflag = 0; /* flag for labelled common declarations */
./reader.c:632: p2->op = NOASG p2->op; /* this was omitted in 11 & /6 !! */
./table.c:128: " movei A1,1\nZN", /* ZN = emit branch */
./xdefs.c:13: * symbol table maintainence
Thus, I'm confident that Jay's work was based on Steve Johnson's
compiler, rather than Alan Snyder's.
Norman Wilson asks:
>> ...
>> How did that C implementation handle ASCII text on the DEC-10?
>> Were it a from-scratch UNIX port it might make sense to store
>> four eight- or nine-bit bytes to a word, but if (as I sense it
>> was) it was C running on TOPS-10 or TOPS-20, it would have had
>> to work comfortably with DEC's convention of five 7-bit characters
>> (plus a spare bit used by some programs as a flag).
>> ...
Our pcc compiler treated char* as a pointer to 7-bit ASCII strings,
stored in the top 35 bits of a word, with the low-order bit normally
zero; a 1-bit there meant that the word contained a 5-digit line
number that some compilers and editors would report. Of course, that
low-order non-character bit meant that memset(), memcpy(), and
memmove() had somewhat dicey semantics, but I no longer recall their
specs.
kcc later gave us access to the PDP-10's 1- to 36-bit byte
instructions.
For text processing, 5 x 7b + 1b bits matched the conventions for all
other programming languages on the PDP-10. When it came time to
implement NFS, and exchange files and data with 32-bit-word machines,
we needed the ability to handle files of 4 x 8b + 4b and 9 x 8b (in
two 36-bit words), and kcc provided that.
The one's-complement 36-bit Univac 1108 machines chose instead to
store text in a 4 x 9b format, because that architecture had
quarter-word load/store instructions, but not the general variable
byte instructions of the PDP-10. Our campus had an 1108 at the
University of Utah Computer Center, but I chose to avoid it, because
it was run in batch mode with punched cards, and never got networking.
By contrast, our TOPS-20, BSD, RSX-11, SunOS, and VMS systems all had
interactive serial-line terminals, and there was no punched card
support at all.
-------------------------------------------------------------------------------
- Nelson H. F. Beebe Tel: +1 801 581 5254 -
- University of Utah FAX: +1 801 581 4148 -
- Department of Mathematics, 110 LCB Internet e-mail: beebe(a)math.utah.edu -
- 155 S 1400 E RM 233 beebe(a)acm.org beebe(a)computer.org -
- Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ -
-------------------------------------------------------------------------------
>> -r is weird because it enables backwards reading, but only as
>> limited by count. Better would be a program, say revfile, that simply
>> reads backwards by lines. Then tail p has an elegant implementation:
>> revfile p | head | revfile
> tail -n can be smarter in that it can simply read the last K bytes
> and see if there are n lines. If not, it can read back further.
> revfile would have to read the whole file, which could be a lot
> more than n lines! tail -n < /dev/tty may never terminate but it
> will use a small finite amount of memory.
Revfile would work the same way. When head has seen enough
and terminates, revfile will get SIGPIPE and stop. I agree that,
depending on scheduling and buffer management, revfile might
read more than tail -n, but it wouldn't read the whole of a
humongous file.
Doug
