The MRBackup Compressor
Version 1.03, 10/13/92

The  compressor is a free-running application typically started by MRBackup
to perform data compression/decompression services.  When MRBackup requires
these  services,  it  enters  into  a  "dialogue"  with the Compressor.  By
separating the compression services from the MRBackup program, the MRBackup
program  is  smaller.   Compression  performance  is  also  enhanced by the
streaming   of  data  to/from  the  compressor  (actual  data  movement  is
minimized).

The  compressor is implemented as a small overlayed program.  Upon startup,
it  first checks to see if a copy of Compressor is already running.  If so,
it  exits  immediately  (only  one instance of Compressor may be run at one
time).  Otherwise, it creates a public port named "MRCompress".  When it is
idle,  very  little memory resources are required.  When it becomes active,
the  primary  code  segment  is "rolled in" and memory is allocated for the
compression/decompression tables.

The  compressor  should  normally  be  kept in the same directory where the
MRBackup  program  is stored.  The logical name "MRBackup:" should point to
this  directory.   If  you  wish to preload the compressor so that MRBackup
will  always  find it available, simply issue the following command, either
from the CLI or from your s:user-startup script:

    RUN <nil: >nil: MRBackup:Compressor

If  you  wish to stop the compressor, just issue the following command from
the CLI:

    MRBackup:Compressor quit

Two  versions  of  the  compressor are provided:  one with overlays and one
without   overlays.    The   overlayed  version,  as  delivered,  is  named
Compressor.   The  non-overlayed version is named "Compressor.No_Overlays".
The  overlayed  version  requires very little memory when it is idle, since
the  compression code segment is removed from memory.  This is normally the
preferred  version  to  use.   However, this also means that the Compressor
program file must be readily accessible so that the overlay segments can be
accessed  quickly.   If  you are in a situation where you must run MRBackup
from  floppy  disk, you may prefer to use the non-overlayed version.  To do
this,  simply  rename  the  overlayed  version to "Compressor.Overlays" and
rename the non-overlayed version to "Compressor".  It's easy to distinguish
between  the  two  versions, even after you've renamed them.  The overlayed
version  will  always  be the (slightly) larger of the two.  This is due to
the additional overlay management code required.