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

 device-name[:][,...]

    Specifies the name of a physical device or a logical name that
    translates to the name of a physical device. The device name
    can be generic: if no controller or unit number is specified,
    any device that satisfies the specified part of the name is
    allocated. If more than one device is specified, the first
    available device is allocated.

 logical-name[:]

    Specifies a string of 1 to 255 alphanumeric characters. Enclose
    the string in single quotation marks (` ')  if it contains
    blanks. Trailing colons (:)  are not used. The name becomes a
    process logical name with the device name as the equivalence
    name. The logical name remains defined until it is explicitly
    deleted or your process terminates.