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

 device-name[:]

    Specifies the name of the device you want to go to.

 directory-spec

    Specifies the name of the directory you want to go to. A
    directory name must be enclosed in brackets ([ ]).  Use the minus
    sign (-)  to specify the next higher directory from the current
    default.

    On Alpha systems, if the length of the resulting default
    directory specification exceeds 255 characters, the SET DEFAULT
    attempts to replace the default directory string with a generated
    directory specification. If this happens, then in addition to
    the normal syntax check, the entire path to that specification,
    including the device, is verified and must exist for the call to
    succeed.

    On Alpha systems, if the process parse style is set to extended,
    then the directory specification may include a directory ID
    (DID).

    You must specify either the device-name parameter or the
    directory-spec parameter. If you specify only the device name,
    the current directory is the default for the directory-spec
    parameter. If you specify only the directory name, the current
    device is the default for the device-name parameter.

    You can use a logical name but it must constitute at least the
    device part of the specification. When you use a search list
    logical name as the parameter, the logical name is not translated
    by the SET DEFAULT command. Instead, the SET DEFAULT command
    retains the logical name so that OpenVMS Record Management
    Services (RMS) is able to access the entire search list. If you
    enter the SHOW DEFAULT command, the search list logical name
    is displayed as the default device, along with its equivalence
    strings.