/sys$common/syshlp/helplib.hlb SHOW, DEVICES, Qualifiers, /BITMAP  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BITMAP ddcu:

    Creates a new table showing all active bitmaps for a given
    device. Included in the display are the size and index number
    of the bitmaps.

    Initially, up to 6 bitmaps can be active on a particular device.

    Note that the SHOW DEVICE/FULL ddcu: display also displays status
    to indicate that bitmaps are active on the device.