https://gunkies.org/index.php?action=history&feed=atom&title=System_call 2026-06-06T13:33:51Z Revision history for this page on the wiki MediaWiki 1.30.1 https://gunkies.org/w/index.php?title=System_call&diff=26737&oldid=prev 2022-06-27T12:27:27Z

<p>Stubby, but a start</p> <p><b>New page</b></p><div>A '''system call''' is the mechanism by which a [[user]]'s computation, usually running in a [[process]], requests that the [[operating system]]'s [[kernel]] perform some service for it. Since the kernel is usually operating in some specially-privileged way (often in a special mode of the [[Central Processing Unit|CPU]], to which the users do not have access, so that they may be protected from each other), the process must use some special mechanism to transfer, in a carefully controlled way, to the kernel.<br /> <br /> This is usually done with a restricted [[instruction]] which causes a [[trap]], but other approaches have been used. For instance, [[Multics]] used a combination of its [[single-level store|single-level memory]] and [[protection ring]]s to do system calls with a [[subroutine]] call into the kernel.<br /> <br /> [[Category: CPU Basics]]<br /> [[Category: OS Basics]]</div>

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