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

    (VAX only) The static system parameter VCC_PTES controls the
    maximum size of the virtual I/O cache. It specifies the potential
    size in pages.

    The virtual I/O cache automatically shrinks and grows, depending
    on your I/O workload and how much spare memory your system has.
    As your I/O workload increases, the cache automatically grows,
    but never to more than the maximum size. When your applications
    need memory, the cache automatically shrinks.

    This special parameter is used by Compaq and is subject to
    change. Do not change this parameter unless Compaq recommends
    that you do so.