question about OS??

Hello, I am kind of new to programming, and one of my courses requires that I study operating systems hence I have started reading up on it on my own...I am very confused on what system calls are?? I have looked it up in several books, which give a very detailed definition, and I couldn not find any internet sites that had a general overview of system calls, but I would really appreciate if someone could give a brief description of what a system call is??? thanks in advance

System calls are used by applications to make requests for resources from the operating system. In most cases the resources being hardware or access to memory.

DISGUISED is absolutely right. here is an example of a few system calls.

Code:

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system("PAUSE");
system("DIR");
system("cd\\");

all require
#inlude <stdlib.h>

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