segmented memory models

[Patrick Finnegan]

On Monday 04 August 2008, Sean Conner wrote:
> It was thus said that the Great Jim Brain once stated:
> > Tony Duell wrote:
> > >No it doesn't, given that a PDP11 address to a program is always
> > > 16 bits. The 18 or 22 bit phuysicall addresses were created by
> > > the MMU.
> >
> > Did an MMU exist for the 8086?
>
>   If such a think existed, it would have been an external circuit,
> and would have been very hard to support since the 8086 did not
> include support for restartable instructions (same situation on the
> 68000).

The PDP-11 doesn't support restartable instructions either.  You don't 
need restartable instructions to support an MMU, only to support 
virtual memory type operations.  For example, my Z80-based Altos 8000 
has a bank-switching MMU that could operate the same way as an MMU on a 
808[68] would.

Pat
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