5 Mar
2025
5 Mar
'25
6:23 a.m.
From: Larry McVoy
Not once did I think about packing, the structs
somehow just worked on
the machines I was working on. Maybe the TCP/IP guys knew about spacing
in the structs.
Not really! Of the first 6 TCP/IP implementations:
https://gunkies.org/wiki/TCP_and_IP_bake_offs
only 1 was in C - and it was a relatively late one. The earliest ones were
mostly in assembler (PDP-10 and PDP-11).
Noel
5 Mar
5 Mar
8:39 p.m.
New subject: Any UNIX With No C In Userland?
Noel Chiappa wrote:
BUT, the basic TCP and IP protocols seem to have been created with a
general care that two byte fields should be aligned at multiples of
two bytes and four byte fields should be at multiples of four bytes,
or at the VERY least, no multi-byte field should cross a four byte
boundary (which would have been a pain to PDP-10 programmers who
likely expected 32 bits of data in each 36 bit word).
IP and TCP Options may blow that out of the water, I don't recall.
ISTR that in the IL protocol (atop IP) in early Plan9, the four byte
sequence numbers would cross over the lines in a traditional RFC box
diagram.
And for early TCP/IP networking and alignment pain (with Unibus!):
I briefly looked at gluing the TCP/IP stack in MIT-ITS for the 2020
(KS10, a PDP-10) which had a Unibus, to the driver someone had written
a Unibus Interlan NI1010 card, BUT the 14 byte Ethernet header meant
the 32-bit words in the TCP and IP headers landed across the (36 bit)
word boundaries expected by ITS' TCP stack (that had been written to
speak to IMPs). There might have been an (MIT added?) BLT to move
8-bit bytes around (or the DEC EXTEND MOVSLJ might have been
available), but it was too gross to contemplate... I suppose Berkeley
trailers might have solved the problem (had I known about them at the
time, but.... also gross).
And as for C: It was born on a 16-bit word system that expected 16-bit
aligned words, replacing B, a language with just the word datatype, on
a system with a 32KB (or less) user space, by people who had just come
from a project where waiting for working production PL/I compiler had
been a major headache, and generally suffered from "second system
syndrome" bloat.
I think it's fair to say that the essence of UNIX and the brilliance
of the development team (largely lost on modern developers) was to
make it as simple as possible, but no simpler.
IMO judging Unix, C and it's creators by criteria like "how could they
not have anticipated my alignment problems" (or why isn't C like PL/I)
is armchair quarterbacking. If you feel otherwise, maybe you should
travel back in time and join the Unix-Haters mailing list, or at least
not be on this one, insulting people who were involved, and are kind
enough to put up with our inane blathering...
From: Larry
McVoy
Not once did I think about packing, the structs
somehow just worked on
the machines I was working on. Maybe the TCP/IP guys knew about spacing
in the structs.
Not really! Of the first 6 TCP/IP implementations:
only 1 was in C - and it was a relatively late one. The earliest ones were
mostly in assembler (PDP-10 and PDP-11). 
6 Mar
6 Mar
4:03 a.m.
New subject: Any UNIX With No C In Userland?
It appears that Phil Budne <phil(a)ultimate.com> said:
Noel Chiappa wrote:
BUT, the basic TCP and IP protocols seem to have been created with a
general care that two byte fields should be aligned at multiples of
two bytes and four byte fields should be at multiples of four bytes,
or at the VERY least, no multi-byte field should cross a four byte
boundary (which would have been a pain to PDP-10 programmers who
likely expected 32 bits of data in each 36 bit word).
There were a bunch of S/360 systems, which also need two- and
four-byte fiekds to be aligned unless you do extra byte string moves
to pack and unpack the structures.
From:
Larry McVoy
Not once did I think about packing, the structs
somehow just worked on
the machines I was working on. Maybe the TCP/IP guys knew about spacing
in the structs.
Not really! Of the first 6 TCP/IP implementations:
only 1 was in C - and it was a relatively late one. The earliest ones were
mostly in assembler (PDP-10 and PDP-11). And as for C: It was born on a 16-bit word system that
expected 16-bit
aligned words, replacing B, a language with just the word datatype, on
a system with a 32KB (or less) user space, by people who had just come
from a project where waiting for working production PL/I compiler had
been a major headache, and generally suffered from "second system
syndrome" bloat.
I believe the earliest versions of C were on a GE 635, a word addressed
machine comparable to a PDP-10. But it moved to a PDP-11 soon enough
where the byte and word addresses motivated the datatypes that turned
B into C.
R's,
John
4:35 a.m.
New subject: Any UNIX With No C In Userland?
On Wed, Mar 5, 2025 at 11:11 PM John Levine <johnl(a)taugh.com> wrote:
This is a startling claim that I have never heard before. Can you cite
a source for this?
The history as recounted in Dennis Ritchie's paper on the history of C
(https://www.nokia.com/bell-labs/about/dennis-m-ritchie/chist.pdf) is
that the initial bootstrapping of PDP-7 Unix was done by
cross-assembling on a GE-635, with paper-tape hand carried to the PDP.
B appears to have been an invention that began life on the PDP-7 and
was subsequently ported to the PDP-11. But C did not appear until they
were solidly on the PDP-11, and was developed on that machine. The
earliest connections to other machines were Dennis Ritchie
constructing a cross-compiler for B that ran on the PDP-7; as he
described it:
|The most ambitious enterprise I undertook was a genuine cross-compiler
|that translated B to GE-635 machine instructions, not threaded code. It was
|a small tour de force: a full B compiler, written in its own language and
|generating code for a 36-bit mainframe, that ran on an 18-bit machine with
|4K words of user address space.
C was later ported to GE-635 and IBM 370, but there's no indication
it was created on the GE-635.
- Dan C
snip
And as for C: It was born on a 16-bit word system that expected 16-bit
aligned words, replacing B, a language with just the word datatype, on
a system with a 32KB (or less) user space, by people who had just come
from a project where waiting for working production PL/I compiler had
been a major headache, and generally suffered from "second system
syndrome" bloat.
I believe the earliest versions of C were on a GE 635, a word addressed
machine comparable to a PDP-10. But it moved to a PDP-11 soon enough
where the byte and word addresses motivated the datatypes that turned
B into C.
5:28 a.m.
New subject: Any UNIX With No C In Userland?
I thought Dennis said he didn’t the work on the 635 but you’re right, C was mostly on the
Pdp-11 and then targeted back to the 635.
Please consider the environment before reading this message.
John Levine, johnl(a)taugh.com
On Mar 5, 2025, at 23:36, Dan Cross
<crossd(a)gmail.com> wrote:
On Wed, Mar 5, 2025 at 11:11 PM John Levine <johnl(a)taugh.com> wrote:
This is a startling claim that I have never heard before. Can you cite
a source for this?
The history as recounted in Dennis Ritchie's paper on the history of C
(https://www.nokia.com/bell-labs/about/dennis-m-ritchie/chist.pdf) is
that the initial bootstrapping of PDP-7 Unix was done by
cross-assembling on a GE-635, with paper-tape hand carried to the PDP.
B appears to have been an invention that began life on the PDP-7 and
was subsequently ported to the PDP-11. But C did not appear until they
were solidly on the PDP-11, and was developed on that machine. The
earliest connections to other machines were Dennis Ritchie
constructing a cross-compiler for B that ran on the PDP-7; as he
described it:
|The most ambitious enterprise I undertook was a genuine cross-compiler
|that translated B to GE-635 machine instructions, not threaded code. It was
|a small tour de force: a full B compiler, written in its own language and
|generating code for a 36-bit mainframe, that ran on an 18-bit machine with
|4K words of user address space.
C was later ported to GE-635 and IBM 370, but there's no indication
it was created on the GE-635.
- Dan C
snip
And as for C: It was born on a 16-bit word system that expected 16-bit
aligned words, replacing B, a language with just the word datatype, on
a system with a 32KB (or less) user space, by people who had just come
from a project where waiting for working production PL/I compiler had
been a major headache, and generally suffered from "second system
syndrome" bloat.
I believe the earliest versions of C were on a GE 635, a word addressed
machine comparable to a PDP-10. But it moved to a PDP-11 soon enough
where the byte and word addresses motivated the datatypes that turned
B into C. 
6:23 a.m.
New subject: Any UNIX With No C In Userland?
Dan Cross writes:
John Levine wrote:
Whilst I agree the claim is startling, there is a connection between
early C and the GE 635. The little known Snyder C compiler has back
ends for the PDP-10, PDP-11, and Honeywell 6000 series (nee GE 635).
https://github.com/PDP-10/Snyder-C-compiler/blob/master/MAC-TR-149.pdf
I believe this compiler was started when Snyder visited Bell Labs in
1973, and it comes with a very archaic version of Yacc.
I believe the earliest versions of C were on a GE
635, a word addressed
machine comparable to a PDP-10. But it moved to a PDP-11 soon enough
This is a
startling claim that I have never heard before. [...] C did
not appear until they were solidly on the PDP-11, and was developed on
that machine. The earliest connections to other machines were Dennis
Ritchie constructing a cross-compiler for B that ran on the PDP-7
7:47 p.m.
New subject: Any UNIX With No C In Userland?
On Thu, Mar 6, 2025 at 1:23 AM Lars Brinkhoff <lars(a)nocrew.org> wrote:
Dan Cross writes:
Interesting. I wonder if this is the basis for Dennis mentioning the
GE-635 port in the C history paper?
- Dan C.
John Levine wrote:
Whilst I agree the claim is startling, there is a connection between
early C and the GE 635. The little known Snyder C compiler has back
ends for the PDP-10, PDP-11, and Honeywell 6000 series (nee GE 635).
https://github.com/PDP-10/Snyder-C-compiler/blob/master/MAC-TR-149.pdf
I believe this compiler was started when Snyder visited Bell Labs in
1973, and it comes with a very archaic version of Yacc. I believe the earliest versions of C were on a GE
635, a word addressed
machine comparable to a PDP-10. But it moved to a PDP-11 soon enough
This is a
startling claim that I have never heard before. [...] C did
not appear until they were solidly on the PDP-11, and was developed on
that machine. The earliest connections to other machines were Dennis
Ritchie constructing a cross-compiler for B that ran on the PDP-7 
5:09 p.m.
New subject: Any UNIX With No C In Userland?
On Wed, Mar 5, 2025 at 11:03 PM John Levine <johnl(a)taugh.com> wrote:
I believe the earliest versions of C were on a GE 635, a word addressed
machine comparable to a PDP-10. But it moved to a PDP-11 soon enough
where the byte and word addresses motivated the datatypes that turne
I believe the history is this.... Ken write the original B
interpreter/subsystem
for in Assembl;er (see the Unix V0 stuff). Dennis
write a new B compiler in B. That was moved the GE635 (and Steve Johnson
brought it with him to Waterloo). When the PDP-11 came, Dennis started
change the compiler to add features for the PDP-11. This was originally
called "New B" (or nb). He used a continuous development scheme.
Originally, nb could accept B, but ass Dennis added more and more features
that were not compatible (basically as typing was added), nb became so
different it was renamed C.
Johnson's comment was that by the time he returned from Waterloo, no one
was using B anymore.
At some point, Synder (who was a summer student) wrote a C compiler for the
PDP-10. I am unclear if that was before the Honeywell 6000 back end,
although given the dates, if you look at the code repositories, I >>think<<
it was. FWIW: by 1978, Dennis and Brian do not mention the PDP-10 on page
179 of K&R — only the PDP-11, Honeywell, IBM 360/370 and Interdata 8/32.
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7 comments
6 participants
participants (6)
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Clem Cole -
Dan Cross -
jnc＠mercury.lcs.mit.edu -
John Levine -
Lars Brinkhoff -
Phil Budne