When we decided to port Unix to 32-bits, there were a number of candidates we looked at, including the IBM-360, the DEC-20, and the Interdata.   The Vax was barely there at the time, and we also felt a bit of pressure to use a non-Dec machine because some manufacturers were muttering about a too-close association of ATT & Dec that was incompatible with our status as a regulated monopoly.  It was also clear that being able to buy compatible Unix machines from several different manufacturers would ultimately drive the prices down and be good for ATT. Dennis hated the channel I/O on the 360, and I hated the little pinhole glimpses of memory that could only be seen by loading a register--that really clashed with the "one flat memory" model in C.  For the DEC-20, the word size was indeed a problem.  We had built a C compiler for the 36-bit Honeywell machine, and it was quite happy to have 9-bit bytes (in fact, their OS supported this).  But at the time, tape drives were the major way large data got into and out of a machine, and they all liked 8-bit bytes.  And there were issues in both C and Unix if the byte size didn't evenly divide the word size (think malloc, unions, sizeof, etc.).  So the 20 was out. The Interdata was a good compromise.  The machine had been used in a lot of flight simulators, etc., so it had a track record.  It was similar to an IBM-360, but had an address mode for addressing memory directly with no base registers.  And we bought the machine with writable microcode, which we had some ideas of playing with. As it turned out, the biggest problems in porting were taking little-endian code and data and putting it on a big-endian machine, dealing with the consequences of having more registers, and the effect of this on process switching and debugging (stack traces, etc.).  The pre-V7 system calls liked to return -1 when there was an error -- V7 wanted to see nulls.  This turned out to be a critical problem -- if an old-style call with -1 got returned and taken to be a pointer, the Interdata generated a double fault--trying to read a word with an odd-byte address, and memory out of bounds.  Sadly, these faults came in several subtics apart, and the result was that the address of the fault got trashed, leaving the machine to resume at location 0 with no hint about how it got there. For this and other reasons, Ken and Dennis invented the header file concept -- previously, the structs that described data structures like inodes were printed in the manual, and copied out by hand when they were used.  By this point, Lint was a going concern, and I hacked a version of Lint that insisted that when a structure was declared more than once, the declarations must come from the same physical location.  This was a big help in rooting out hidden obsolete structure definitions and forcing the use of header files. The port ended up being fairly successful.  The connection with Interdata less so.  At one point there was a meeting attended by me, Dennis, Ken, and several managers.  We went to Interdata and met in a building that used to be a bank -- the meeting room was in the old vault.  We told Interdata what we had done, and  gave them some information about the growth of Interest in Unix.  We then said that the machine needed some fixes before we could deploy a general-purpose system on it -- the -1 botch was the biggie, because we could not have a broken user program turn the machine into a stone.  Interdata listened politely.  Several days later they said 'not interested". One thing I noticed over the years is that there are very few people who, having done one Unix port, were willing to do another.  I certainly wasn't interested.  After the first time, there is little to learn, and the tedium of debugging a compiler and OS on a bare machine, when the documentation of the machine was hastily written and often incomplete, was frustrating almost beyond describing.  So it was another group in Bell Labs that jumped on the Vax and made an effective and lasting 32-bit port. Steve ----- Original Message ----- From: "Arthur Krewat" &lt;krewat(a)kilonet.net&gt; To:<tuhs@minnie.tuhs.org> Cc: Sent:Mon, 18 Sep 2017 11:30:19 -0400 Subject:Re: [TUHS] PDP-10 UNIX? On 9/17/2017 10:34 PM, Johnny Billquist wrote: PDP-10? PDP-10, hit person, I for one would be VERY interested. It would be an interesting exercise to try it out on a SIMH emulator. know. like 9 bits would work - and still, waste 4 bits of the 36-bit word ... any code carried over from elsewhere would never use the 9th bit unless you know of stuff that does? And yup, I remember KLH, not personally, but as the KLH-10 author :)

On Mon, Sep 18, 2017 at 01:25:41PM -0400, Clem Cole wrote: Wussies, I did it twice :) Not really true, I worked a port to the ETA-10 and managed a group that was doing a bringup on a MIPS chip (Cobalt Qube). I had more of a clue the second time around, actually quit over it. The details, if you care, were that I was brought in as the director of software, there was no VP, I reported to the CEO. I was assured that I would be treated like a founder, yada yada. OK, some time goes by and the CEO wants a schedule. Be aware that things were a mess, no backups, no nightly builds, no source control, engineers were hoarding "their" code on their machines. It was little disfunctional, but I was straightening all that out, had it pretty much under control by the time they asked for a schedule. We were using GCC which hadn't had a ton of MIPS time under its belt, and Linux, which was in the same state. We could boot a kernel but it crashed (I think, this was a long time ago). Anyway, they wanted a fast schedule (don't they always?) and I looked around and said "6 months". Which was aggressive but I felt it was doable, the kernel was booting, once you get that stable, userland tends to fall into place. We were also developing a web interface to the box, that was the whole point, it was a "web server in a box" with a web UI, no login for you (well there was but we weren't supposed to use it). They freaked at the schedule. "The board will never go for that!" So I called Bill Earl, who has done more bringups on MIPS chips than anyone, period. At least so far as I knew at the time, still don't know of anyone who has done more. He asked a bunch thoughtful questions and said "weeeeell, maybe you could do it in 3 months. If you don't hit any bugs." I asked "Would you bet your kids college education on it?" He said "Oh, hell no, I wouldn't bet $20 that you'll make it in 3 months. You hit one compiler bug, that could blow the whole schedule easy." So I go back to the CEO and said "6 months". He's all pissed and says he'll take it to the board. I say I want to be there to make my case. He says "Nope, you aren't an executive." I handed in my resignation. Founder my ass. --lm