OAK CD :0, Руководство пользователя

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What is SCSI?
The following brief description of SCSI does not set out to fully cover
SCSI in depth, but rather deals with SCSI in the context of the
Archimedes and the Oak SCSI controller card.
SCSI, (Small Computer Systems Interface) is a high speed interface
designed to connect a variety of peripherals to a host system (the
initiator - so called because it initiates the SCSI commands). Up to 7
devices may be attached to one host, with each device having a unique
SCSI ID number (0 to 7). The default ID for the Oak SCSI controller
card is 7, leaving 0-6 free for peripherals. One SCSI device may
actually be responsible for controlling more than one peripheral. For
example, the Adaptec hard disc controller card can control two ST506
winchesters, but appears as just one SCSI device, with the two drives
being differentiated by the Logical Unit Number [LUN]. Thus the first
drive may appear to the initiator as SCSI ID 3, LUN 0 and the second
drive as SCSI ID 3, LUN 1.
SCSI devices are `daisy chained' together, i.e. they are all connected
together in parallel to one 50 way bus. SCSI devices should therefore
provide 2 SCSI connections, effectively a `SCSI in' and a `SCSI out'
to allow further devices to be attached to the bus.
SCSI winchester drives include their own `in built' winchester
controller which is optimised for that particular drive, and thereby
allows the winchester manufacturer to employ a variety of techniques
to maximise both the storage capacity and the speed of the drive. Thus
SCSI winchesters are generally much faster than their equivalent
ST506 counterparts which interface to a standard ST506 controller.
Also, because of their on-board `intelligence' SCSI winchesters are
much easier to set up and use as they deal with their own defect
management, and `know' their own shape (No of heads, cylinders etc).
SCSI has an 8 bit data bus, and is capable of transferring data at a
maximum rate of roughly 2Mb/sec in asynchronous mode. This
maximum figure is limited in practice by the performance of the
peripheral. For example, a fast, modern 20Mb winchester would
typically be able to achieve a data transfer rate of 650Kb/sec
(compared with a 20Mb ST506 winchester at roughly 300Kb/sec), and
a fast 300Mb winchester would achieve close to 1.5Mb/sec. On the
bulk of SCSI systems, however, performance is degraded most by the
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