第一章
Introduction
An
operating systen is a program that manages the computer hardware.
The
hardware—the central processing unit(CPU), the memory, and the
input/ouput(I/O) devices – provides the basic computers resources
for the system.
The
application programs—such as word processors, spreadsheets,
compiler, and Web browsers—define the ways in which these resources
are used to solve users' computing problems.
The
operating system controls the hardware and coordinate its use among
various application programs fir the various users.
A
more common definition, and the one that we usually follow, is that
the operating system is the one program running at all times on the
computer—usually called the kernel.
Softeare
may trigger an interrupt by executing a special operation called a
system call.
On
a single-processor system, there is one main CPU capable of excuting
a general-purpose instuction set, including instructions from user
processes.
Multiprocessor
systems(also known as parallel systems or tightly coupled systems)
are growing in importance. Such systems have two or more processors
inclose communication, sharingthe computer bus and sometimes the
clock, memory, and peripheral devices.
A
trap (or an exception) is software-generated interrupt caused either
by an error(for example, division by zero or invalid memory access)
or by a specific request from a user program that an operating-system
service be performed.
User
mode amd kernel mode(also called supervisor mode, system mode, or
privileged mode). A bit, called the mode bit, is added to the
hardware of the computer to indicate the current mode : kernel(0) or
user(1).
Embedded
systems almost always run real-time operating system. A real-time
system is used when rigid time requirements have been placed on the
operation of a processor or the flow of data.
The operating system is responsible for the following activities in connection with process management
i)Scheduling processes and threads on the CPUs
ii)Creating and deleting both user and system processes
iii)Suspending and resuming processes
iv)Providing mechanisms for process synchronization
v)Proving mechanisms for process communication.
The operating system is responsible for the following activities in connection with process management
i)Scheduling processes and threads on the CPUs
ii)Creating and deleting both user and system processes
iii)Suspending and resuming processes
iv)Providing mechanisms for process synchronization
v)Proving mechanisms for process communication.
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