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

  INITIALSIZE = e

     e  Is a numeric expression whose value specifies the
        number of blocks in the initial allocation of space
        for a new file on a disk.  Defaults to no initial allocation.

  If you do not specify INITIALSIZE or if you specify zero, no
  initial allocation is made.  The system attempts to allocate
  contiguous space for INITIALSIZE.  If not enough contiguous space
  is available, noncontiguous space is allocated.

  INITIALSIZE is effective only at the time the file is created.  If
  EXTENDSIZE is specified when the file is created, the value
  specified is the default value used to allocate additional storage
  for the file.  If you specify EXTENDSIZE when you open an existing
  file, the value you specify supersedes any EXTENDSIZE value
  specified when the file was created, and remains in effect until
  you close the file.  Unless specifically overridden, the default
  EXTENDSIZE value is in effect on later openings of the file.