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

       /PARALLEL[=n]

    Lists the records with differences side by side. The value of
    the parameter n specifies the number of matched records to merge
    after each unmatched record; it must be a non-negative decimal
    number less than or equal to the number specified in the /MATCH
    qualifier.

    By default, the DIFFERENCES command does not list records after
    each list of unmatched records. Also by default, the DIFFERENCES
    command creates only a list of merged differences.