DECC$PIPE_BUFFER_QUOTA

   OpenVMS Version 7.3-2 adds an optional fourth argument of type
   int to the pipe function to specify the buffer quota of the
   pipe's mailbox. In previous OpenVMS versions, the buffer quota
   was equal to the buffer size.

   DECC$PIPE_BUFFER_QUOTA lets you specify a buffer quota to use
   for the pipe function if the optional fourth argument of that
   function is omitted.

   If the optional pipe fourth argument is omitted and DECC$PIPE_
   BUFFER_QUOTA is not defined, then the buffer quota defaults to
   the buffer size, as before.

   Default: 512

   Minimum: 512

   Maximum: 2147483647