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Unformatted text preview: e to memory (in DMA transfer). This
interrupt is actually caused by the interrupt handler software. The interrupt handler
sends an interrupt signal to the appropriate device driver to wake it up so that it
can take the further course of action.
2. Device Drivers. There is a device driver for each type of device connected to
the system. For example, a system normally has a disk driver for disks, a printer
driver for printers, a tape driver for tapes, and so on. The device driver contains
all device-dependent code. A device driver accepts abstract I/O requests from the
device-independent software layer above it, and translates it into commands for
the appropriate device controller. It then writes these commands and their
associated parameters into the controller's registers.
Device-independent Software. This layer of software performs the I/O
functions that are common to all devices, and provides a uniform interface to the
user-level software. It takes care of mapping symbolic device names on to the
appropriate device driver. Some I/O devices, such as disks, are sharable in the
sense that they can be used by many users at the same time. Other devices, such
as tapes and printers, have to be dedicated to a single user until that user has
finished using it. The device-independent software layer handles both shared and
dedicated devices in such a manner that avoids problems.
4. User-level Software. This layer of software contains the standard I/O system
calls in the form of library procedures. The users use these system calls, such as
read, write, print, send, and receive for performing the desired I/O operations.
SECURITY We saw towards the beginning of this chapter that security in computer systems
deals with protecting the various resources and information of a computer system
against destruction and unauthorized access. A total approach to computer security
involves both external and internal security. External security deals with securing
the computer system against exte...
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This document was uploaded on 04/07/2014.
- Spring '14