Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!nuchat!sugar!karl
From: karl@sugar.hackercorp.com (Karl Lehenbauer)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Virtual Memory / doable 1.4 request
Message-ID: <3877@sugar.hackercorp.com>
Date: 27 May 89 06:55:09 GMT
References: <8905200449.AA20664@postgres.Berkeley.EDU> <3856@sugar.hackercorp.com> <3859@sugar.hackercorp.com>
Organization: Sugar Land Unix - Houston
Lines: 29

In article <3859@sugar.hackercorp.com>, peter@sugar.hackercorp.com (Peter da Silva) writes:
> In article <3856@sugar.hackercorp.com>, karl@sugar.hackercorp.com (Karl Lehenbauer) writes:
> > Bummer.  You can't do mapped files without an MMU.  That means mapped files
> > would be not work with non-MMU Amigas.  OK, you *could* do it if you didn't
> > demand page the file in on non-MMU machines but rather copied the whole
> > thing in on first open and then wrote the whole thing out on last close and 
> > maybe at checkpoint intervals or whatever.  It's sick, I know.
 
> Actually VMS allows you to specify this sort of mapped file as well as the
> more normal sort, so I guess there MUST be some use for it.

Now that you mention it, this was known as "permanent common" on Plato.  It
consisted of data space you could write into, and you could set it up to
checkpoint periodically as well as the write-on-close business.  It was pretty
cool.  The first line of your program could be "number_of_access++", or the
Tutor (ick) equivalent, and as long as you had initialized it properly,
it would count number of entries to your game, or whatever.  I would use
this for some things if it was available on the Ami, like a records section,
etc.  What, another AllocMem memory type?  It's not that hard to read it in
and write it out explicitly anyway.

Any RSX-11M/plus people out there remember when DEC added this write-out-on-
close capability to RSX and didn't tell anybody?  Our software relied on
being able to get cold images of the commons from the load file, and did its 
own checkpointing.  Needless to say it, broke in a big way, and was kind of
hard to find...
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