Re: IIgs RAM drive question

[dempson@actrix.gen.nz (David Empson)]

David. E. Goble <goble@kin.on.net> wrote:

> dempson@actrix.gen.nz (David Empson) wrote:
> >
> >There is a second RAM disk which is provided by ProDOS-8 itself in
> >auxiliary memory (S3,D2), called "/RAM".  This RAM disk cannot be used
> >to boot ProDOS-8, and its contents is not preserved over restart.  It is
> >unavailable in GS/OS.
> >
> Hi David;
> 
> Can you tell me more about /RAM, like "what, when, where, how" :> This
> is the first time I have heard of it. Thanks.

/RAM is available on every IIgs, IIc and 128K IIe while running any
version of ProDOS-8.  It appears as S3,D2 and is almost 64KB in
capacity.  Its contents occupy all of auxiliary memory except the text
screen and part of zero page.  ProDOS creates this RAM disk
automatically when it boots.  Its contents are not preserved over a
reboot, and you can't boot from it.

If an application wants to use auxiliary memory for its own purposes, it
can disable the /RAM disk through a well defined procedure.  Most large
applications like AppleWorks do this, so you won't see mention of a
"/RAM" volume in this sort of program.  ShrinkIt is another example, but
IIPlus.Unshrink and IIPlus.ShrinkIt leave the /RAM volume available.

There are a few differences between /RAM and other volumes.  For
example, the root directory only occupies a single block instead of four
blocks, which means you can't save more than twelve files on /RAM unless
you use subdirectories.  (The root directory limit is 51 files for any
other volume.)

Another special feature is that the driver automatically creates the
directory when the /RAM volume is formatted.  For all other volumes, the
formatting software has to do this itself.

Finally, there is a special method supported by the driver for reserving
the double hi-res graphics buffer area ($2000-$3FFF for page 1, and
$4000-$5FFF for page 2, which is not used as often).  If the first file
saved to /RAM is exactly 8KB in size, its data area will cover the first
auxiliary hi-res page.  Saving a second 8KB file will cover the second
auxiliary hi-res page.  This allows an application to refer directly to
the auxiliary hi-res pages without risking interference with other files
saved to /RAM.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand