# Process Identifier ![rw-book-cover](https://readwise-assets.s3.amazonaws.com/static/images/article2.74d541386bbf.png) ## Metadata - Author: [[wikipedia.org]] - Full Title: Process Identifier - Category: #articles - Summary: A process identifier (PID) is a unique number used by operating systems to identify active processes. In Unix-like systems, new processes are created using the fork() system call, and the PID helps manage these processes. Windows also uses PIDs, with specific numbers assigned to important system processes like the System Idle Process. ## Highlights - In [Unix-like](https://en.wikipedia.org/wiki/Unix-like) operating systems, new processes are created by the `[fork()](https://en.wikipedia.org/wiki/Fork_(operating_system))` [system call](https://en.wikipedia.org/wiki/System_call). The PID is returned to the [parent process](https://en.wikipedia.org/wiki/Parent_process), enabling it to refer to the child in further function calls. The parent may, for example, wait for the child to terminate with the `[waitpid()](https://en.wikipedia.org/wiki/Waitpid())` function, or terminate the process with `[kill()](https://en.wikipedia.org/wiki/Kill())`. ([View Highlight](https://read.readwise.io/read/01jw799fepf0zc19vnhmyte4ke)) - In [computing](https://en.wikipedia.org/wiki/Computing), the **process identifier** (a.k.a. **process ID** or **PID**) is a number used by most [operating system](https://en.wikipedia.org/wiki/Operating_system) [kernels](https://en.wikipedia.org/wiki/Kernel_(operating_system))—such as those of [Unix](https://en.wikipedia.org/wiki/Unix), [macOS](https://en.wikipedia.org/wiki/MacOS) and [Windows](https://en.wikipedia.org/wiki/Windows)—to uniquely identify an active [process](https://en.wikipedia.org/wiki/Process_(computing)). ([View Highlight](https://read.readwise.io/read/01jv2zpmwpkxbyaqpvqeqpem6x)) - This number may be used as a parameter in various function calls, allowing processes to be manipulated, such as adjusting the process's priority or [killing](https://en.wikipedia.org/wiki/Kill_(command)) it altogether. ([View Highlight](https://read.readwise.io/read/01jv2zpqmapmnrcsjv8psy5kr7))