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| OPERATING
SYSTEM _ INTRODUCTION |
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| System
Calls: |
System
calls provide an interface to the services made available
by an operating system. These calls are generally
available as routines written in C and C++ or using
some assembly-language instructions. Processes are
using operating systems calls heavily for its proper
execution.
Application programming Interface (API) specifies
a set of functions that are available to an application
programmer, including parameters that are passed to
each function and the return values the programmer
can expect.
Examples are:
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Win32 API – for Windows Systems |
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POSIX API – for Unix, Linux and Mac OS
X |
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Java API – for Java Virtual Machine |
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The
functions that make up an API typically invoke the
actual system calls on behalf of the application programmer.
For example, the Win32 function CreateProcess() actually
calls the NTCreateProcess() system call in the Windows
kernel.
The run-time support system for most programming languages
provides a system-call interface that serves as the
link to system calls made available by the operating
system. The system-call interface intercepts function
calls in the API and invokes the necessary system
call within the operating system.
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The handling
of a user application invoking the open( ) system
call |
The
caller needs to know nothing about how the system
call is implemented or what it does during execution.
It just needs to obey the API and understand what
the operating system will do as a result of the execution
of that system call.
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| Types
of System Calls: |
System
calls can be grouped roughly into five major categories:
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Process Control |
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end, abort |
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load,
execute |
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create
process, terminate process |
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get
process attributes, set processes attributes |
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wait
for time |
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wait
event, signal event |
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allocate
and free memory |
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File Management |
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create
file, delete file |
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open,
close |
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read,
write, reposition |
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get
file attributes, set file attributes |
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Device
Management |
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request
device, release device |
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read,
write, reposition |
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get
device attributes, set device attributes |
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logically
attach or detach devices |
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Information
Maintenance |
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get time or date, set time or date |
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get system data, set system data |
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get process, file, or device attributes |
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set process, file, or device attributes |
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Communications |
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create, delete communication connection |
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send, receive messages |
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transfer status information |
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attach or detach remote devices |
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