# Green threads

> Many operating systems provide an API for creating new threads. This model where a language calls the operating system APIs to create threads is sometimes called 1:1, meaning one operating system thread per one language thread.

> Many programming languages provide their own special implementation of threads. Programming language-provided threads are known as green threads, and languages that use these green threads will execute them in the context of a different number of operating system threads. For this reason, the green-threaded model is called the M:N model: there are M green threads per N operating system threads, where M and N are not necessarily the same number
> [Using Threads to Run Code Simultaneously - The Rust Programming Language](https://doc.rust-lang.org/book/ch16-01-threads.html)

:programming:
