Re: Ada's Slide To Oblivion ...

[Matthew Woodcraft <mattheww@chiark.greenend.org.uk>]

nickroberts@ukf.net (Nick Roberts) writes:

> On Fri, 08 Feb 2002 12:23:48 GMT, Ole-Hjalmar Kristensen
> <oleh@vlinux.voxelvision.no> wrote:

> >> David Brown wrote:
> >> On, say, a high end PDP-11, or a 68000, or an 8086 (but not its
> >> progeny!), code space and data space are physically separate.  There
> >> are wires that come out of the processor to say which space to use.  On
> >> such a system there's NO WAY to write to code space, and it's not
> >> impossible that

> It is not fantasy, but I think factually slightly imperfect.
>
> As far as I recall, neither the 8086 nor the 8088 (nor any of their
> progeny) ever had this kind of control signal.

A genuine 8086 had two pins which indicated the segment register which
had been used to calculate an address. I imagine an 8088 did too.

I suppose this could reasonably be used to separate code space from data
space if all the code were in ROM. I also once saw a suggestion that it
could be used to have a separate stack space.

-M-