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OTHER RELATED CONCEPTS
Before concluding this chapter, we will have a look at a few concepts related to
input/output devices. Several of these concepts are useful to understand how I/O devices
are connected to and communicate with a computer system.
We saw in Chapter 7 that all the components of a computer communicate with the
computer's CPU through the system bus. That means the I/O devices need to be attached
to the system bus. However I/O devices are not connected directly to the computer's
system bus. Instead, they are connected to an intermediate electronic device called a
device controller, which in turn is connected to the system bus. Hence a device controller is an interface unit between an I/O device and the system bus. On one side, it knows how
to communicate with the I/O device connected to it, and on the other side, it knows how
to communicate with the computer's CPU and memory through the system bus.
A device controller need not necessarily control a single device, rather a single device
controller can usually control multiple I/O devices. It comes in the form of an electronic
circuit board (also known as an electronic card) that plugs directly into the system bus,
and there is a cable from the controller to each device it controls. The cables coming out
of the controller are usually terminated at the back panel of the main computer box in the
form of connectors known as ports. Figure 9.37 illustrates how I/O devices are connected
to a computer system through device controllers.
Using device controllers for connecting I/O devices to a computer system instead of
connecting them directly to the system bus has the following advantages:
1. A device controller can be shared among multiple I/O devices allowing many I/O
devices to be connected to. the system.
2. I/O devices can be easily upgraded or changed without any change in the computer
3. I/O devices of man...
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- Spring '14