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WRITING A DRIVER
5-14
5
by the driver -- specifically, command queuing. If you choose to follow the
rules for multiple callers, the firmware queues command packets for you
whenever the bus is busy.
For example, if a user of the SCSI interface only has disk applications, only a
SCSI disk driver for the particular operating system may need to be written. If
the rules for multiple callers are used, then at a later time, a SCSI tape driver
for the same operating system may be added without affecting the old disk
driver (assuming that the tape driver returns are vectored through a different
vector than the SCSI disk driver). Refer to the Interface Rules for Multiple Callers
section in this chapter for details.