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From: rhood@pro-gsplus.cts.com (Robert Hood)
Newsgroups: comp.sys.apple2
Subject: Re: 800k Partition on RAM
Message-ID: <1991Jun18.123835.14109@crash.cts.com>
Date: 18 Jun 91 12:38:35 GMT
Sender: root@crash.cts.com
Organization: Crash TimeSharing, El Cajon, CA
Lines: 55

In-Reply-To: message from whitewolf@gnh-starport.cts.com

Hmmm - I was just looking over the "800K partition on a 1Meg card" problem
and I think I have a solution.  However, it's a kluge and would have to be
manually adjusted...I think.  (Chris Scherrer: I would have addressed this
to you, but I didn't see your address.)
 
The problem, IMO, lies in the bitmap.  It is rather simple to make the
RAMdisk into an 800K version as opposed to a 1024K version - all you have
to do is alter the number of blocks available on the disk and adjust the
bitmap accordingly.  Any copy of _Inside Apple ProDOS_ should give all the
information needed - and it works; I did the same thing to make my 5.25"
drives run 320 blocks.
 
Making the other 224K usable is another problem altogether.  What I
suggest, for maximum use of the RAMdisk at least work, is this:
 
Use your AE utility to configure your RAMdisk to 832K.  (This is really
only needed if the AE utility will create a companion 192K RAMdisk with the
rest of the RAM.)  The 832K ramdisk will have 1664 blocks - exactly 64 more
than you need.  You'll have to go in and remove them - make the RAMdisk
forget about them.
 
The volume bitmap for that RAMdisk will be 208 bytes long, and resides in
block 6 of the RAMdisk.  Get a block editor and read that block.  I believe
free blocks are represented by 1, and used ones by 0.  What you have to do
is change the last eight $FF bytes (offsets $0C8 through $0CF) to $00
values.
 
Now you have 1600 blocks available - minus the seven used by ProDOS. 
That's half the battle.  Next you have to change the number of blocks
recorded as being on the disk from $680 to $640.  Unfortunately, there is
where my knowledge runs out - it's been too long ago.  Try scanning for a
hex $06 and see if there's an $80 nearby - I think that's what I did at
first.  To check to see if those are the right locations to change (once
you've found them), compare those values to the same locations on a 5.25"
disk - the 5.25 will have $01 and $18 where the RAMdisk has $06 and $80.
 
When you find the right pair, change the $80 to a $40.  This will make the
RAMdisk truly 800K - you'll lose 32K by this method, unfortunately.
 
There's one other thing I'm worried about - Andy Nicholas can advise you on
this, though.  I don't know how ShrinkIt determines how to shrink a disk -
the entry in the device list will list your RAMdrive _as_ a RAMdrive, and I
don't know if ShrinkIt will shrink an 800K RAMdrive identically to an 800K
3.5 drive.  (Andy, can you clear this up?)
 
Oh well - if you have questions, email me.  Or if you think the echo would
benefit, post 'em.  However, I answer email more quickly - and more
reliably.  :)
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