system defines that system’s general structure. For each type of interrupt, separate
segments of code in the operating system determine what action should be taken. An
interrupt service routine is provided that is responsible for dealing with the interrupt.
1.5.1
Dual-Mode Operation
In order to ensure the proper execution of the operating system, we must be able to
distinguish between the execution of operating-system code and user- defined code.
The approach taken by most computer systems is to provide hardware support that
allows us to differentiate among various modes of execution.
At the very least, we need two separate
modes
of operation:
user mode
and
kernel
mode
(also called
supervisor mode
,
system mode
, or
privileged mode
).
Figure 1.10: Transition from user to kernel mode.
1.5.2 Timer
We must ensure that the operating system maintains control over the CPU. We cannot
allow a user program to get stuck in an infinite loop or to fail to call system services
and never return control to the operating system. To accomplish this goal, we can use a
timer
. A timer can be set to interrupt the computer after a specified period. The period
may be fixed (for example, 1/60 second) or variable (for example, from 1 millisecond
to 1 second).
15
Operating Systems I- Lecture
Lecturer: Dr. Sura Z. Alrashid
1.6
Process Management
1.7
Memory Management
1.8
Storage Management
To make the computer system convenient for users, the operating system provides a
uniform, logical view of information storage. The operating system abstracts from the
physical properties of its storage devices to define a logical storage unit, the
file
. The
operating system maps files onto physical media and accesses these files via the
storage devices.
1.8.1
File-System Management
1.8.2
Mass-Storage Management
1.8.3
I/O Systems
1.8.4 Caching
Caching
is an important principle of computer systems. Information is normally kept
in some storage system (such as main memory). As it is used, it is copied into a faster
storage system—the cache—on a temporary basis. When we need a particular piece of
information, we first check whether it is in the cache. If it is, we use the information
directly from the cache; if it is not, we use the information from the source, putting a
copy in the cache under the assumption that we will need it again soon.
Because caches have limited size,
cache management
is an important design problem.
Main memory can be viewed as a fast cache for secondary storage.
1.9
Protection and Security
1.10 Distributed Systems
A distributed system is a collection of physically separate, possibly heterogeneous
computer systems that are networked to provide the users with access to the various
resources that the system maintains. Access to a shared resource increases computation
speed, functionality, data availability, and reliability.
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