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STACKER NOTE                       Stac Electronics Technical Note

Subject: Performance differences between Stacker software and
         coprocessor versions.

Tech010- 2/20/92
Page 1 OF 1
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STACKER's software version is supplemented and enhanced by the
coprocessor card.  The STACKER coprocessor card yields the highest
compression of data, the smallest device driver and the fastest I/O.

Note: For a coprocessor install checklist, see tech008.

Q: What types of performance increases will I see with the
   coprocessor ?
A: 1. Hardware compression offers as much as 10-20% more disk
      space;
   2. Disk reads and writes are 5-15% faster;
   3. The higher performance is especially apparent on slower
      machines.
   4. The device driver memory requirements with the card are
      as little as 14k vs. 26k for the software version.

Q: What is the difference between the XT/8 coprocessor and the
   AT/16 ?
A: 1. The AT/16 is a 16 bit card designed for At class
      machines such as 286, 386 and 486s.  The XT/8 is an 8 bit card 
      designed for XT class machines.
   2. The AT/16 uses an I/O address whereas the XT/8 requires a 16 K 
      upper memory address.  Note: on 386/486 machines, the XT/8
      requires its 16K upper memory range to be excluded from use 
      by memory managers.  Neither card requires an IRQ.
   3. Both coprocessors incorporate the same compression chip so 
      they will achieve the same amount of compression.

Q: What if some hardware conflict prevents the coprocessor from
   functioning ?
A: If the coprocessor card does not install correctly or load at
   boot time, STACKER will still run ("Coprocessor card not
   functioning--invoking software driver") and data will still be
   both compressed and accessible.  You would just be operating
   without the benefits of the card.

*Upgrading to the coprocessor version from software only:*

Upgrading from the software to the coprocessor version does not
require re-installing STACKER.  However, only those files written
to the drive with the coprocessor benefit from the higher
compression.  With version 2.0, the files can be recompressed
using SDEFRAG with the /R parameter.  Recompressing the files
under version 1.x requires that the files be reloaded into the
Stacker drive.

