1. Init
   1. Modes
      1. 0
         1. Shutdown (halt)
      2. 1
         1. Admin single user mode
            1. Chỉ root user có thể login
      3. 2
         1. Multi user mode (có NFS)
      4. 3
         1. Multi user mode (ko NFS)
      5. 4
         1. ko xài
      6. 5
         1. Multi Users (graphic mode) (X11)
      7. 6
         1. Reboot
2. Login
3. GUI
   1. X Window service
4. Network
   1. Login từ xa
5. Network File System
   1. SUN phát triển
   2. Transparent
      1. Mạng = máy đơn
6. multiuser
7. multiproccessing
8. multitasking