MAXBUF sets the maximum allowable size for any single buffered
    I/O packet. Buffered I/O packets are allocated from the
    permanently resident nonpaged dynamic pool. The terminal,
    mailbox, and printer device drivers are examples of device
    drivers that perform buffered I/O.

    The number of bytes specified in the I/O request plus the size of
    a driver-dependent and function-dependent header area determine
    the required buffered I/O packet size. The size of the header
    area is a minimum of 16 bytes; there is no absolute upper limit.
    However, this header area is usually a few hundred bytes in size.

    The default value on Alpha and Integrity servers continues to be
    8192.

    The maximum value of MAXBUF is 64000 bytes.

    MAXBUF is a DYNAMIC parameter.