3.2. Device interfacing
In this section the basics of how devices are controlled by program are given. Figure 3.1 gives an operating system context for all the levels associated with I/O handling.
Figure 3.1. Device-handling subsystem overview.
In Section 2.5 it was pointed out that programs running above the operating system must be prevented from programming devices directly. This section will show how this restriction can be enforced and how users may request input or output by making a system call, since they are not allowed to program it for themselves (see Section 3.4). Figure 3.1 indicates this difference in privilege between the operating ...
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