VMS Help INITIALIZE, Qualifiers, /SIZE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SIZE=n

    Specifies the size of the DECram disk (device type DT$_RAM_DISK)
    to be allocated from available memory. The size of the device is
    created at disk initialization time.

    To deallocate space, specify /SIZE=0. All resources specifically
    allocated to the DECram disk are returned to the system.

    Note that n cannot exceed 524,280 blocks either on a VAX system
    or on versions of DECram prior to Version 2.3. DECram Version
    2.3 running on an Alpha system supports up to 67,108,864 blocks,
    equivalent to 32GB.