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From: dbfunk@icaen.uiowa.edu (David B Funk)
Newsgroups: comp.sys.apollo
Subject: Re:  Are 425s REALLY memory hogs?
Summary: 68040 uses 4Kb page size
Keywords: 68040, 4Kb pagesize
Message-ID: <6391@ns-mx.uiowa.edu>
Date: 8 Jun 91 03:43:23 GMT
References: <9106051356.AA08687@richter.mit.edu>
Sender: news@ns-mx.uiowa.edu
Organization: Iowa Computer Aided Engineering Network, University of Iowa
Lines: 40

In article <9106051356.AA08687@richter.mit.edu> krowitz@RICHTER.MIT.EDU (David Krowitz) writes:
>What is *really* disturbing is that not only is the virtual address
>size (SZ) much larger, but the physical RAM size (RSS) is larger!
>340Kb to run "sleep"?! It's no more than a 100 line program!
>
>One thing comes to mind ... I think I remember reading (where?) that
>the segiment size (size of the chunks of memory which the MMU maps
>into RAM) had been increased from 32Kb with the 68020/68030 MMU's to
>256 Kb with the 68040 MMU. Of course, I'm getting old and grey, and
>I can't be relied upon to remember the exact numbers (or even the
>correct answer ;-) ).
>

Yes, the sr10.3 release notes state this change. This is because the
MMU in the 68040 chip (which is a subset of the 030 MMU) supports only
two possible page sizes, 4Kb & 8Kb; thus Apollo was forced to use a larger
page size on the 040 machines. As the address translation cache is smaller,
they also went to a larger segment size, to reduce cache misses (I think ).
From page 1-44 in the sr10.3 release notes:

     The /bin/ld and /com/bind linkers use new segment and page sizes, as
     follows:

        o The segment size has changed from 32 KB to 256 KB.

        o The page size has changed from 1 KB to 4 KB.

     Programs linked with the pre-SR10.3 linkers may load slower on a
     Series 400 workstation.  Specifically, the text sections are copied at
     load time instead of being mapped into memory. This causes a slower
     load time and allows the possibility of scribbling on text.

Note that the page size on the "010/020/030 only" machines (all DNxxx series
except DN5500) is still 1Kb. It is only the 040'able machines that
use the larger page size (9000/4xx).

These changes will result in larger memory allocation granularity, and thus
the "growth" of the process size.

Dave Funk