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From: esf00@amdahl.amdahl.com (Elliott S. Frank)
Newsgroups: comp.arch
Subject: Re: What should be in hardware but isn't
Message-ID: <15042@amdahl.amdahl.com>
Date: Fri, 25-Sep-87 14:28:19 EDT
Article-I.D.: amdahl.15042
Posted: Fri Sep 25 14:28:19 1987
Date-Received: Sun, 27-Sep-87 01:46:38 EDT
References: <581@l.cc.purdue.edu> <18336@amdcad.AMD.COM> <582@l.cc.purdue.edu> <14750@watmath.waterloo.edu>
Reply-To: esf00@amdahl.amdahl.com (Elliott S. Frank)
Organization: The Beige Building Full of Bright Engineers, Inc.
Lines: 31

>In article <582@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
>>BTW, there is an address modification procedure which is missing on all
>>machines I have seen except the UNIVAC's.  That is to consider the register
>>file as a memory block and allow indexing on it.  Another missing procedure
>>is to enable the register file to be treated as a block of memory so that
>>bytes or short words can be addressed.  These two operations can be combined

In article <14750@watmath.waterloo.edu> ccplumb@watmath.waterloo.edu (Colin Plumb) writes:

> ...PDP-10...
>           the first (as far as I know) machine to have a register file.

The feature was part of the UNIVAC SS-90 and the 110x machines (all which
[architecturally] predate the founding of DEC). It may be in the SS-80,
too (but that machine was before my time :-)).

It is one of the ultimate cases of providing a hardware feature where
the implementation ignores the architecture. (Can you say `dependant
upon a side effect'?)  The UNIVAC 1108 assumed (if memory serves me
right) that indirect addressing would reference the memory
`masked' by the registers.  Direct references to the memory locations
accessed the registers.  Two different access modes referring to the
same location referenced two different objects!
-- 

Elliott S Frank    ...!{hplabs,ames,sun}!amdahl!esf00     (408) 746-6384
               or ....!{bnrmtv,drivax,hoptoad}!amdahl!esf00

[the above opinions are strictly mine, if anyone's.]
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