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From: hassinger@lmrc.uucp (Bob Hassinger)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Files larger than available memory (scrolling editor history)
Message-ID: <8104@lmrc.uucp>
Date: 25 Sep 90 10:47:12 GMT
References: <924@ucsvc.ucs.unimelb.edu.au> <1990Sep23.174736.16118@lavaca.uh.edu>
Organization: Liberty Mutual Research Center, Hopkinton, MA
Lines: 39

In article <1990Sep23.174736.16118@lavaca.uh.edu>, jet@karazm.math.uh.edu (J. Eric Townsend) writes:
> In article <924@ucsvc.ucs.unimelb.edu.au> U3364521@ucsvc.ucs.unimelb.edu.au (Lou Cavallo) writes:
>>the discussion re: Virtual Memory/MMU/Protection reminds me of a tangentially
>>related issue.  Some criticism of Amiga software (such as word processors) is
>>related to the inability to deal with files/data larger than available memory.
> 
...
> 
> It can be done.  It's somewhat bizarre, but it can be done.  Essentially,
> you keep track of the changes to the file.  You change the file whenever
> you reach one of a set of conditions:
> -- size of changes > some default size
> -- user is not doing anything (cycle stealing, of a sort :-)
> -- user goes forward or backwards in the file some distance > x
...

It sure can be done!  In fact it has been done at least since the mid-60s on
DECtape/LINCtape based systems (no disk at all).  The classic editor for the
LINC-8 worked in this way - and quite well too everything considered.

If you have virtual memory you just allocate as much as you need in a
conventional editor (ref: VMS EDT or TPU for example).  If you do not have
virtual memory you use this "scrolling editor" scheme that has been around on
machines FAR smaller and slower than the Amiga for 25 years.  There is a
classic paper (in one of the IEEE journals I think) on the LINC design.

Note too the LINC design was later successfully ported to OS/8 on the PDP-8 and
PDP-12 where the file system did not even support dynamic extension of files
and later yet to RT-11 on the PDP-11 (KED) where the file system was only a
little more cooperative.

If it could be done on a 4K LINC-8 with a single LINCtape, is certainly could
be done a 512K Amiga with floppies that are several times bigger and many times
faster!

(Remember the famous quote about the fate of those or forget history...)

Bob Hassinger
hassinger@lmrc.UUCP