Description: ProDOS: Using /RAM and Double High-Resolution Graphics
Header: ProDOS: Using /RAM and Double High-Resolution Graphics

 Whenever ProDOS is booted, it checks the environment; if ProDOS finds a 128K
 Apple II system, it configures the auxiliary 64K memory bank as a RAM disk
 named /RAM.  This "disk" is catalogued as slot 3, drive 2, since it's
 comprised of memory on the 80-column card in slot 3.

 If you plan to use this auxiliary memory for high-res graphics, you must
 protect yourself from /RAM.  To construct a space for protecting high-res
 pages in auxiliary memory while maintaining /RAM as an online storage device,
 perform the following two steps:

 1.  Save a "dummy" 8K file as the first entry in /RAM; this file
    will always be saved at $2000 to $3FFF.

 2.  Immediately afterwards, save a second "dummy" 8K file to
    /RAM; this file will be saved at $4000 to $5FFF.

 --> IMPORTANT NOTES:

 1.  There is no formula for determining where the blocks of /RAM
    physically reside in memory.

 2.  The logical blocks in /RAM are not physically contiguous.

 3.  There is no guaranteed way to protect any other fixed
    portions of auxiliary memory by means of the "dummy" file
    method.

 If you wish to protect all auxiliary memory not reserved for use by Apple, you
 must disconnect /RAM.  The following three areas of the system global page are
 of interest to anyone who wishes to disconnect /RAM:

          $BF10-$BF2F contains the disk device driver addresses.
          $BF31 contains the number of devices minus one.
          $BF32-$BF3F contains the list of disk device numbers.
 Apple Technical Communications


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