[TUHS] First Unix-like OSes not derived from AT&T code?

[Larry McVoy]

On Mon, May 02, 2022 at 09:16:40AM -0700, Bakul Shah wrote:
> On May 2, 2022, at 8:43 AM, Clem Cole <clemc at ccc.com> wrote:
> > 
> > Thoth Thucks....   [Kelly Booth gave me one of these tee's years go].
> > 
> > Mike Malcolm did not try to clone UNIX - for one thing, it was in B [which Steve Johnson has spread the gospel of same on his sabbatical).  It was not until the Thoth rewrite that became QNX that they tried to ensure all of the Unix behaviors and APIs.  Mike was certainly had an influence by UNIX and IIRC his thesis and the Thoth papers reference/compare it.
> 
> IIRC Gordon Bell and Dan Dodge worked with Thoth as students but QNX is not derived from it. I ran across QNX at a contract job in 1986 or so[1]. Back then it fit in 8KB. IIRC the original few versions were mostly written in assembly language or had substantial portions in assembly while most of Thoth was written in C[2]. The original QNX was basically a message passing microkernel. Unix APIs came in much later.

I was friends with Dan Hildebrandt, one of the 3 people allowed to commit
changes to the microkernel in the 1990's.  That history seems pretty
accurate though Dan told me the commonly used microkernel code fit in 4K
of instruction cache, I don't recall what it needed in the data cache.
Dan told me they were very careful to not let that bloat, I remember
him saying "the instruction cache needs to have space for user code".
A refreshing point of view, especially since I was living in "I measured
it, it's only 1% slower" AKA "death by a thousand paper cuts".