Can anybody explain what a Ruby Fiber is and how that works under the hood? Is this like green threads which are backed by N OS threads, like Go? Or does this

Can anybody explain what a Ruby Fiber is and how that works under the hood? Is this like green threads which are backed by N OS threads, like Go? Or does this all happen using a single thread? Does the Ruby VM knows to suspend execution of the Fiber on a blocking operation? I guess there's an epoll somewhere there too, right?