How do OS X terminal sessions persist through reboots?

Being an avid Linux user prior to buying a MacBook Pro, I typically have several terminal tabs open at any one time. In the past, crashes and reboots would generally trash my workflow, and the majority of my respective tab histories. I searched for ways to solve this problem but always came up empty; aside from various techniques that utilised combinations of tools like ssh, screen, tmux, and required a virtual private server (or similar). One of my favourite things about using my MacBook Pro for writing scripts, and using CLI tools, etc; is that my terminal sessions persist beyond crashes and reboots by default. In fact, I just restored a backup from almost 2 years ago, and when I logged in for the first time, I was presented with my old desktop and three bash shells that comprised a project that I was working on all that time ago. I would like to know how OS X makes this feature possible. Does anybody here have insight into how it works?