Matt Thomas wrote:

> At 03:44 PM 3/18/2004, Perry E. Metzger wrote:
>
>> "Toru Nishimura" <locore32@gaea.ocn.ne.jp> writes:
>> > The introduction of "supervisor mode" was a mystery.   Someone will 
>> disclose
>> > the (real) story behind it.
>>
>> It was introduced to try to get DEC to adopt it for its new machines,
>> I thought, since VMS needed it.
>
>
> Nope.  ULTRIX was always kernel/user and didn't use the supervisor or
> executive modes of the VAX.  Therefore there was no reason to have them
> in MIPS.  VMS was never ever going to run on MIPS so it wasn't added for
> that reason.
>
>

I have it from our chief architect, who did work at DEC in the past, 
that there was indeed at some point a plan/hope to port VMS off the VAX 
and onto a new RISC architecture. MIPS Computer Systems was pitching for 
this business with its upcoming R4000, and while VMS apparently used 4 
rings of protection, it was thought that maybe these could be shoehorned 
into 3 rings, hence the addition of supervisor mode. But the R4000 lost 
out in the end, and DEC decided to do its own internal CPU development, 
which became Alpha.

-- 
                         Nigel Stephens         mailto:nigel@mips.com
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