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Unformatted text preview: oller idea for each device. It uses a generic device
controller (called SCSI controller) on the computer system and allows any device with an
SCSI interface to be directly connected to the SCSI bus of the SCSI controller. The SCSI
interface of a device contains all circuitry that the device needs to operate with the
As shown in Figure 8.27, a SCSI controller connects directly to the computer bus on one
side and controls another bus (called SCSI bus) on the other side. Since the SCSI
controller is connected to the computer's bus on one side and to the SCSI bus on the other
side, it can communicate with the processor and memory and can also control the devices
connected to the SCSI bus. The SCSI bus is a bus designed for connecting devices to a
computer in a uniform way. In effect, the SCSI controller extends the computer's bus
outside the main system box and allows other devices to be connected to the computer
with the help of this extended bus. The important thing about the SCSI bus is that there is a standard protocol for sending device control messages and data on the bus. Each device
connected to the SCSI bus has a standard SCSI interface (a single chip) that knows about
the bus protocol.
Since SCSI extends the computer's bus outside the main computer box, it allows any
SCSI device to be connected to the computer without the need to open the computer box
and install a device controller on its internal bus. Bringing the computer's bus directly
into the drive allows even higher data-transfer rates than are possible with ESDI. A SCSI
being an extension of a computer's bus, it can accommodate multiple devices
simultaneously. Most current implementations of SCSI limit the number of devices to
seven due to the bus capacity limitation. Moreover, SCSI being an extension of the bus,
any type of device (hard-disk drive, optical-disk drive, tape drive, printer, plotter,
scanner, etc.) can be linked (or daisy-chained) on a single SCSI port (see Figure 8.27).
As the name implies, SCSI starte...
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This document was uploaded on 04/07/2014.
- Spring '14