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      STACKER NOTE                                         STACKER NOTE
                        STACKER DRIVER SIZE IN MEMORY
                          (Applies to Stacker 4.0)
      STAC FAX  4517 (05-24-1994)
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      BACKGROUND
      
      The Stacker device driver is a memory resident program. Your
      system's configuration determines how much space the driver takes
      in conventional memory (the first 640K RAM). The major factors
      affecting the driver's size are whether your system can use DOS
      Protected Mode Services (DPMS), and the size of the drive you are
      compressing. Note that Stacker runs as a block device driver, and
      is usually loaded into conventional memory. However, it is also
      eligible to be loaded into the upper memory blocks just like any
      other device driver. See StacFax 4105 for information on loading
      Stacker high.
      
      WHAT SIZE WILL THE STACKER DRIVER BE?
      
         - Determine if your system can use DPMS
         - Determine which cluster size your system will use
         - Determine the approximate size of the Stacker driver
         - Other factors affecting driver size
           
      Determine if your system can use DPMS
      
      Versions of DOS that support preloading compression drivers also
      allow the use of DPMS. Generally, MS-DOS 6.x, Novell DOS 7, and
      PC-DOS 6.x with file dates after 9-30-93 support preloading.
      Using DPMS, a portion of the driver is loaded into a "protected"
      area of Extended Memory. This significantly reduces Stacker's
      driver size in conventional memory. In order to be sure that your
      system is using DPMS, examine your CONFIG.SYS file. Look for the
      line:
      
              DEVICE=C:\STACKER\DPMS.EXE
      If the line is present, Stacker is making use of DPMS. The line
      will automatically be inserted for you during Setup if your DOS
      version supports preloading.
      
      Determine which cluster size your system will use
      
      The size of the Stacker driver is affected by the cluster size it
      uses during Setup. This in turn is determined by the size of the
      drive you are compressing. As a rule of thumb you may expect the
      following cluster sizes at the default compression ratio of
      2.5:1: A physical drive less than 205MB will use 8K clusters. A
      physical drive between 205MB and  419MB will use 16K clusters. A
      physical drive over 420MB will use 32K clusters. These boundaries
      are not exact and your system may vary. See StacFax 4505 for
      details on cluster size. The Stacker driver uses more memory with
      larger cluster sizes.
      
      In order to determine which cluster size your system is using
      type:
      
           CHECK /D drive:
      where drive: is the drive letter of your Stacker drive. Locate
      the column "Stacker Drive x:". At the bottom of that column will
      be a statistic "Bytes per Cluster". This is the cluster size your
      system is using for that Stacker drive. If you have more than one
      Stacker drive, the size of the Stacker device driver is
      determined by the largest cluster size used.
      
      Determine the approximate size of the Stacker driver
      
      The Stacker driver uses conventional memory approximately as
      follows:
      
                8K Clusters     16K Clusters       32K Clusters
      With DPMS     16K             24K               40K
      Without DPMS  44K             53K               71K
      One Kilobyte = 1024 bytes.
      
      Other factors affecting driver size
      
      These numbers are approximate because other factors also affect
      the driver size. These include the number of drives you compress
      and whether you turn on Automounting for a removable drive. The
      driver will also be significantly larger (about 8.3K) if you are
      not using DPMS and do not have the line DOS=HIGH in your
      CONFIG.SYS file. Each Stacker drive you compress will add about
      560 bytes to the Stacker driver. Automounting also adds about 560
      bytes per drive. Also, DPMS itself uses about 2K of conventional
      memory.
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      Copyright 1994 Stac Electronics
