VMS Help MERGE, Specification File Qualifiers, /WORK_FILES, Full Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    You can improve the performance of Sort by placing work files
    on different disk-structured devices. Using the /WORK_FILES
    qualifier in a specification file to reassign work files makes
    it unnecessary to make logical assignments prior to invoking Sort
    at the command or program level.