ACP_SYSACC

   ACP_SYSACC sets the number of directory file control blocks
   (FCBs) that are cached for disks mounted with the /SYSTEM
   qualifier. Each directory FCB contains a 16-byte array containing
   the first letter of the last entry in each block of the directory
   (or group of blocks if the directory exceeds 16 blocks). Since
   entries in a directory are alphabetical, the cached FCB provides
   quick access to a required directory block. This parameter value
   should be roughly equivalent to the number of directories that
   are in use concurrently on each system volume. It might be
   overridden on a per-volume basis with the /ACCESSED qualifier
   to the DCL command MOUNT. The value should be kept low in systems
   with small physical memory and little file activity, because
   the FCBs require a significant amount of space in the nonpaged
   dynamic pool.

   Too small a value causes excessive XQP I/O operations, while too
   large a value causes excessive physical memory to be consumed by
   the FCB caches.

   ACP_SYSACC is an AUTOGEN and DYNAMIC parameter.