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From: Stephen Fuld <sfuld@alumni.cmu.edu.invalid>
Newsgroups: comp.arch
Subject: Re: base and bounds, Why I've Dropped In
Date: Sun, 15 Jun 2025 14:39:06 -0700
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On 6/15/2025 12:44 PM, John Levine wrote:
> According to Stephen Fuld  <sfuld@alumni.cmu.edu.invalid>:
>> [ base and bounds vs paging
>> An interesting question is whether it is worthwhile to do both.
> 
> Multics had segments of variable size, with each segment paged.
> That worked, give or take the inevitable problem of running out of
> address bits.

I didn't know that about Multics.  Thanks John.  ISTM that their 
approach is the opposite of Unisys's approach.  They put the pages 
within the base and bounds, whereas Unisys puts the base and bounds 
"over" the pages.  I think the Mill's approach is to put them "side by 
side".

I don't want to use the word segments, as that has bad connotations that 
aren't relevant here.  For historical reasons, Unisys uses the word 
"bank" to describe the logical addresses between the base and the bound.


> I think that is an insoluble problem with base and bounds.  However
> you divide up the address space into sections, some sections will
> be too small.

I don't think so.  Probably with the Multics approach, but not with the 
Unisys approach.  You can make the individual "sections"/banks as large 
as you want.


-- 
  - Stephen Fuld
(e-mail address disguised to prevent spam)