Indicates the number of blocks in the initial storage allocation
  (extent) for a disk file.  It takes the following form:

  INITIALSIZE = e

     e  Is a numeric expression.

  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.