Re: Pi4 to Pi5 migration

On Mon, 17 Jun 2024 17:02:37 +0100
The Natural Philosopher <tnp@invalid.invalid> wrote:

Very hard to put a decent Unix on a 286 - Venix was the only one, I
recally.  No memory management.

XENIX was available for the 8086 and the 80286.

Altos used to make a surprisingly usable XENIX machine with an 8086
main processor and a pair of Z80B IO processors (one for the serial ports,
one for the tape and disc). They kept this basic architecture while
upgrading processors (80286+2x8086, 80386+2*80186).

The 80286 had a protected mode with memory management but did not
supply any means to exit from it so the transition to kernel side
unprotected mode had to be done by calling on the keyboard controller to
reset the processor - code then checked a flag location for the value that
said this wasn't a cold boot.

the 386 made porting unix pretty simple. SCO unix was extremely stable.

It certainly did.

Wasn;'t that a Xenix evolution?

Yes SCO bought XENIX from Microsoft, then when they switched to the
SysVR4 codebase (AT&T pulled in everything they could from XENIX and BSD)
they got to rename it to Unix. The earlier XENIX was also rock solid IME on
PC or Altos hardware.

--
Steve O'Hara-Smith
Odds and Ends at http://www.sohara.org/
For forms of government let fools contest
Whate're is best administered is best - Alexander Pope