[TUHS] V7/8086 I'm a bit behind the times here, but...

[Peter Jeremy]

On 2003-Jul-01 18:16:27 -0400, Steve Nickolas <usagi.tsukino at pinku.zzn.com> wrote:
>I already had some ideas, and when I saw something called "v7upgrade", a weird thought came to my head...
>
>I'm wondering if any gurus out there would be able to point me in the
>general direction, as far as getting V7 stuff running on an 8086,
>perhaps a full V7 system.  Something like v7upgrade but including a
>kernel and bootloader.  I don't know.  Just musing...

I've also been considering this in the background ever since "ancient"
Unix became available.  At least one other person has posted that they
did actually do a suitable port.

Downsides:
- 8086 has no hardware protection.  You'd need to go to the 80286 to
  get any inter-process protection.
- 80x86 16-bit memory management is far more primitive than the PDP-11.
  Given the requirement for data and stack addresses to be in the same
  address space (assumed by virtually all C programs), the total data+
  heap+stack space required for a process must be pre-allocated and
  there is no protection between heap and stack.

The main reason I've never proceeded is the lack of a suitable C
compiler: 16-bit 80x86, open source, able to run in 64K I+D mode, and
generating half-way decent code.  (Without the last requirement, the
kernel and some of the larger userland utilities will probably be too
large).

Supporting overlays would add the requirement to handle mixed-mode
code, support segment overrides and 'far' objects.

Peter