VMS Help SCA, SCA Topics, Glossary, physical_library  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    A single directory containing an SCA database. The directory
    should not contain anything else. SCA always locks an entire
    physical library when it accesses it. When you are reading a
    physical library (for example, with a FIND command), other users
    are not allowed to write to the physical library, but other users
    are allowed to read the physical library. When you are writing
    to a physical library (for example, using LOAD), no other user is
    allowed to read or write to the physical library.