3.5. User-level input and output
Low-level mechanisms for performing input and output have been described in some detail. Application programs are, in general, not allowed to program at this level, and must ask the operating system to do I/O on their behalf. We now consider this top-down application-driven view of I/O programming, shown in Figure 3.12.
Figure 3.12. Top-down invocation of I/O.
A general point is that I/O statements should be made as general as possible. Ideally, a given program should be written with I/O statements that can be bound to different devices for a given execution. The language-level I/O is in terms of logical devices ...
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