Library /sys$common/syshlp/pca$help.hlb ATTACH, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The ATTACH command allows you to connect your terminal to another
    process. Using the ATTACH command, you can switch control back
    and forth between several different active processes. To create
    additional processes, use the SPAWN command from within PCA or at
    DCL level.