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Groups > comp.sys.apple2.programmer > #1308

Re: 80 column card RAM disk

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On 02/09/2014 10:15 PM, David Empson wrote:
> Minor correction: it is a seedling file (one data block, no index block)
> when initially created, but it gets converted to a sapling file (one
> index block and up to 256 data blocks) when the length is set to 8192
> bytes. That causes the index block to be allocated, then the rest of HGR
> page 1 to be allocated as data blocks.

Whoops.  My bad.  I did mean sapling file but either my brain or my 
fingers decided to use seedling instead.  :)

> That would be a bad choice since /RAM has probably been arranged this
> way since ProDOS was introduced, and the volume bitmap should be located
> via the directory header.
>
> I'd only expect this sort of behaviour from directory repair utilities,
> and there probably isn't much call for repairing /RAM (if it is even
> available - the utility might need to disable /RAM to use auxiliary
> memory itself).

It is unfortunate that /RAM has to be handled as a special case but that 
is the way it is.  Programs that assume that the root directory is four 
blocks long and uses blocks 2-5 or assume that the volume bit map starts 
at block 6 will always have problems with /RAM.  Not to mention that 
anything that tries to write to blocks 0, 1 and 4-7 will be surprised to 
find that their data has disappeared if they didn't get an error from 
trying to do so in the first place.  :)

> That increases my suspicion that the tech note is out of date and the
> implementation details changed at some point.
>
> My copy of the tech note has an asterisk and footnote saying that block
> 3 is synthesized. That wouldn't be necessary if they allocated a full
> 512 bytes to it.

I'm not sure where my tech notes are at present but I'll have to look 
them up again.  It might be that block 3 only uses the first 16 bytes of 
$0E00-$0FFF as I seem to recall a lot of random stuff in there when I 
looked at it.  Unlike the directory block that was zeroed out.

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80 column card RAM disk ivan@ivanx.com - 2014-09-01 15:05 -0700
  Re: 80 column card RAM disk dempson@actrix.gen.nz (David Empson) - 2014-09-02 11:41 +1200
    Re: 80 column card RAM disk dempson@actrix.gen.nz (David Empson) - 2014-09-02 11:44 +1200
      Re: 80 column card RAM disk Jeff Blakeney <CUTjeffrey_blakeney@yahoo.ca> - 2014-09-02 07:53 -0400
    Re: 80 column card RAM disk Jeff Blakeney <CUTjeffrey_blakeney@yahoo.ca> - 2014-09-02 07:46 -0400
      Re: 80 column card RAM disk dempson@actrix.gen.nz (David Empson) - 2014-09-03 14:15 +1200
        Re: 80 column card RAM disk Jeff Blakeney <CUTjeffrey_blakeney@yahoo.ca> - 2014-09-02 22:36 -0400
          Re: 80 column card RAM disk Antoine Vignau <antoine.vignau@laposte.net> - 2014-09-05 14:27 -0700
  Re: 80 column card RAM disk Jeff Blakeney <CUTjeffrey_blakeney@yahoo.ca> - 2014-09-01 20:09 -0400

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