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

[sbdocker@acs.ucalgary.ca (Sean Brendan Dockery)]

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.

[ ... ]

That would make the amount of free room would be $7A00 (31232) bytes
when BASIC.SYSTEM is still in memory and protected by the ProDOS
bitmap.

|SHRINKIT is much larger than this.  Because of this problem, it is
|also supplied with a small pre-loader called SHRINKIT.SYSTEM, which
|loads at $2000, relocates itself below $2000, then loads the main
|SHRINKIT program (which causes no problems now that BASIC.SYSTEM is
|out of the way).

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.

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".

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.

[ The gauntlet falls... ]

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...

|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.  :)

The technotes (ProDOS 8 technote #23: ProDOS Changes and Minutia)
states two things about ProDOS 8 v1.9:

o Pre-ProDOS 8 v1.9 QUIT code could not load system files larger than
  38K in size (even though there is 39.75K free).  Any type SYS file
  could still be loaded from the selector as long as it was smaller
  than 38K.  Since that version, system files up to 39.75K are
  loadable.

o ProDOS 8 v1.9 and beyond no longer requires a file with a .SYSTEM
  extension to be online at boot-up; if no .SYSTEM file exists, ProDOS
  will enter its file selector menu (where you can select a SYS file
  without a .SYSTEM extension if you wish).

I don't believe that SHRINKIT is larger than 38K in size.  So, it
should* be launchable from the pre-v 1.9 selector.

*: "should" is used provisionally until some graciously grabs my left
   foot and sticks it in my mouth if(when) the SHRINKIT file is found
   to be larger than 38K.

|David Empson                                                               
|dempson@swell.actrix.gen.nz                                                
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