/sys$common/syshlp/helplib.hlb FORTRAN, Statements, OPEN, EXTENDSIZE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  EXTENDSIZE = e

     e  Is a numeric expression whose value specifies
        the number of blocks to extend a disk file when
        additional file storage is allocated.  The space
        used to extend a file is contiguous if possible
        otherwise, noncontiguous space is used.  Defaults
        to the system default for the device.