Re: .SYSTEM file extensions (was Re: Old IIc needs new chipset)

[foegelle@sleepy.cc.utexas.edu (Michael Foegelle)]

In article <Aug02.211715.34110@acs.ucalgary.ca> sbdocker@acs.ucalgary.ca (Sean Brendan Dockery) writes:
>In article <1993Aug2.105937.5110@actrix.gen.nz>
>dempson@swell.actrix.gen.nz (David Empson) writes:
>
>|buffers (about $9200 if you have no files open).
>                ~~~~~
>Actually $9A00.  $9600-$99FF is BASIC.SYSTEM's general purpose buffer
>(which is used to garbage collection in Applesoft among other things),
>but I don't believe that it is protected in the ProDOS memory usage
>bitmap table.
>
  It doesn't matter if it's protected by Prodos, it's Basic.system that
is doing the loading.  To do that, it opens ANOTHER buffer ($9200-$9600)
and then tries loading the file in the intervening space from $2000-$9200
and gives an error if the file is longer than $7200 bytes.

>[ ... ]
>I think that the SHRINKIT.SYSTEM file zeroes all memory usage in the
>ProDOS bitmap except for ProDOS itself.  That way when it tries to
>load the SHRINKIT file at $2000, the overwrite of BASIC.SYSTEM code is
>no longer considered a memory violation.

Of course it does!  The Basic.System program no longer 'exists' in memory
because it gave up control to another system program.  The BI frees its
space in the bitmap (or is supposed to) not the next program that gets
loaded.

>
>Also, perhaps "unspoken rule" was an incorrect way of saying what I
>was trying to express.  It think that a better choice of words might
>have been "unspoken convention".
>
Well, it may be >your< unspoken convention, but I can't say that there's
any consensus on the subject, and since it has never been documented by
Apple as a necessary limitation to system files, it doesn't exist.

>I was referring to the size of files with a .SYSTEM extension.  I
>don't believe that I have ever seen one larger than $7A00 bytes.  This
>would mean that you could run any files with a .SYSTEM extension from
>the BASIC.SYSTEM prompt.
>
Just because you've never seen them doesn't mean they don't exist.  Then
again, most programs get divided into sub-components since they're usually
supplied together on a disk and it's easier to do that way.  For Shrinkit
to be a useful utility for the telecommunications novice it is somewhat
essential that it be contained in one simple to use file.

>Now, to be standing corrected, someone has to give me an example of a
>type SYS file with a .SYSTEM extension that exceeds $7A00 bytes in
>size (without conveniently renaming one).  Anyone, anyone, anyone,
>anyone...
That's totally absurd!  The only time the .SYSTEM part of the filename
has ANY effect on its loading is if it is the first .SYSTEM file in the
root directory at boot time.  Beyond that, Prodos, Basic.System, or any
other program could care less what the filename is as long as it's a SYS
file.
>
>|If you're using a program selector such as Birds Better Bye or the
>|ProDOS 1.9+ selector, then there is no problem launching SHRINKIT
>|directly.  The SHRINKIT.SYSTEM file is only required if you want to
>|launch SHRINKIT from BASIC.SYSTEM.
>
>You should read the technotes more closely.  Either that or try to
>speak more clearly.  :)
>   >Technotes deleted<

So, there was a bug (feature? =) in earlier versions of Prodos that didn't
allow the maximum system file size to be loaded.  So what?  Doesn't have
anything to do with the discussion above.

>
>|David Empson
>|dempson@swell.actrix.gen.nz
>--
> internet: dockery@griffin.cuc.ab.ca
>      -or- sbdocker@acs.ucalgary.ca
>      -or- dockery@pro-calgary.cts.com
> pro-line: dockery@pro-calgary

Michael Foegelle

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