Groups > comp.sys.apple2.programmer > #1300

80 column card RAM disk

Newsgroups	comp.sys.apple2.programmer
Date	2014-09-01 15:05 -0700
Message-ID	<96730f4e-8bc7-4603-9159-2f1dbbaaf37f@googlegroups.com> (permalink)
Subject	80 column card RAM disk
From	ivan@ivanx.com

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I found this in section A.5 of the ProDOS 8 Tech Ref manual:

"The Apple lie computer can optionally contain an Extended 80-Column Text Card, giving the computer access to an additional 64K of RAM. (The Apple lie has the equivalent of such a card built in.) ProDOS uses this extra RAM as a volume, just like a small disk volume. This volume is initially given the name /RAM, but it can be renamed. The 64K of RAM on the card is logically partitioned into 127 512-byte blocks of information. The contents of these blocks are:
Blocks 00-01 Unavailable
Block 02 Volume directory
Block 03 Volume bit map
Blocks 04-07 Unavailable
Blocks 08-126 Directories and Files"

I thought it was interesting that blocks 4-7 are unavailable, since ProDOS would certainly allow them to be used for files. Then it occurred to me that maybe this was to protect the text page, so you can still use, you know, 80 columns; seems like a viable theory.

What I don't get is the math. At 512 bytes per block, block 4 would correspond to $800, not $400. And the text page is only 1K, whereas 2K are reserved (I guess that could be for text page 2; is that used)?

Mostly just curious. Anyone have any insight into this?

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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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