Overview
¾ The two main jobs of a computer are I/O and
processing. In many cases, the main job is I/0, and the processing is merely
incidental.
¾
For instance,
when we browse a Web page or edit a file, our immediate interest is to read
or enter some information, not to compute an answer.
¾
The role of the
operating system in computer I/O is to manage and control I/O operations and I/O
devices.
¾
Although related
topics appear in other chapters, here we bring together the pieces to paint
a complete picture of I/O.
¾
The control of
devices connected to the computer is a major concern of operating-system
designers.
¾
Because I/O
devices vary so widely in their function and speed (consider a mouse, a hard
disk, and a CD-ROM jukebox), varied methods are needed to control them.
¾
These methods
form the I/O subsystem of
the kernel which separates the rest of the kernel from the complexities of
managing I/O devices.
¾
I/O-device
technology exhibits two conflicting trends. On the one hand, we see increasing
standardization of software and hardware interfaces.
¾
This trend helps
us to incorporate improved device generations into existing computers and
operating systems.
¾
On the other
hand, we see an increasingly broad variety of I/O devices.
¾
Some new devices
are so unlike previous devices that it is a challenge to incorporate them into
our computers and operating systems.
¾
This challenge
is met by a combination of hardware and software techniques.
¾
The basic I/O
hardware elements, such as ports, buses, and device controllers, accommodate a
wide variety of I/O devices.
¾
To encapsulate
the details and oddities of different devices, the kernel of an operating
system is structured to use device-driver modules.
¾ The device
drivers present a uniform device – access interface to the I/O subsystem,
much as system calls provide a standard interface between the application and
the operating system.
References
- The Operating System Concepts by Silberschatz, Galvin, Gagne, 8th Edition
No comments:
Post a Comment