Subject: Re: NetBSD/pdp10 ?
To: Perry E. Metzger <>
From: Lars Brinkhoff <>
List: port-vax
Date: 03/07/2002 12:38:35
"Perry E. Metzger" <> writes:
> Brian Chase <> writes:
> > NetBSD/pdp10 anyone?
> The machine only had 18 bit pointers. It is a little light in terms
> of real memory space -- only about a megabyte in a full Moby.

Those machines are clearly not suitable for a NetBSD port.  Maybe
2.11BSD? :)

> Extended PDP-10 architectures have been built

I think many of the PDP-10 machines still in runnable condition would
be extended PDP-10s: KL10 model B, Systems Concepts clones, TOAD-1s.
The exception is of course the DECSYSTEM-2020 with the KS10 processor.

> I was rather fond of the processor series -- byte pointers were NEAT,
> and if you really want to purge C, the fact that not all pointers are
> the same length on a PDP-6 or PDP-10 is a big frightening change for C
> programmers.

This is not an issue in the GCC port.  All pointers are exactly 36

    * Byte pointers (char *, short *, etc) are in the one-word global
      byte pointer format supported in hardware in the extended
      architecture: the 6 most significant bits hold a "P&S" code, and
      the 30 least significant bits hold a word address.

    * Word pointers (int *, float *, double *, etc) are in the global
      address word format.  The 6 most significant bits are always
      zero, and the 30 least significant bits hold a word address.

In some cases local (18-bit) addressing will be used as an optimization,
but this is not visible to the programmer.

Lars Brinkhoff     Linux, GCC, PDP-10,
Brinkhoff Consulting    HTTP programming