The job of an operating system is to share a computer among multiple programs and to provide a more useful set of services than the hardware alone supports. The operating system manages and abstracts the low-level hardware, so that, for example, a word processor need not concern itself with which type of disk hardware is being used. It also multiplexes the hardware, allowing many programs to share the computer and run (or appear to run) at the same time. Finally, operating systems provide controlled ways for programs to interact, so that they can share data or work together.

This is a draft text intended for a class on operating systems. It explains the main concepts of operating systems by studying an example kernel, named xv6. xv6 is a re-implementation of Dennis Ritchie’s and Ken Thompson’s Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, but is implemented in ANSI C for an x86- based multiprocessor.

Contents

1. Operating system interfaces
2. Operating system organization
3. Page tables
4. Traps and system calls
5. Interrupts and device drivers
6. Locking
7. Scheduling
8. File system
9. Concurrency revisited
10. Summary