VMS Help Sys Parameters, ACP_FIDCACHE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    ACP_FIDCACHE sets the number of file identification slots cached.
    A specification of 1 means no cache. Too small a value causes
    excessive XQP I/O operations, while too large a value causes
    excessive physical memory to be consumed by the FID caches.

    ACP_FIDCACHE is a DYNAMIC and FEEDBACK parameter.