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<title>System calls and library calls</title>
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<h1>System calls and library calls</h1>
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<p>
I have wondered for sometime what the difference is between
system calls (found in section 2 of the man pages)
and library calls (in section 3).
Its simple...
<ul>
<li>system calls are provided by the <i>system</i>
and are executed in the system kernel. They are entry points
into the kernel and are therefore NOT linked into your
program. These are not portable
calls.
<li>Library calls include the ANSI C standard library and are
therefore portable. These functions are linked into your program.
</ul>
It is worth noting that, because system calls are part of the
O/S. The program has to make a context switch to the kernel
when they are called and because of this, they have a high
startup overhead. The upside is that the time executing these
routines is assigned to the OS and not the user program.
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<address>Martin Leslie
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