1. Advanced Operating Systems (CS 202)
Presenter today: Khaled N. Khasawneh
Instructor: Nael Abu-Ghazaleh
Jan, 11, 2016

2. Today
Introduction to xv6

3. v6 Sixth Edition Unix a.k.a. Version 6 Unix
First public release of Unix out of Bell Labs
By Ken Thompson & Dennis Ritchie, 1975
Designed for DEC PDP-11*
Original source code still available:

4. Why not using v6 PDP11 is not used nowadays
Missing some of the key issues in modern Oses
Paging
Multicore
Luckily ..

5. xv6 xv6 is an MIT reimplementation of Unix v6 Runs on x86
But we will run it on top of QEMU
Smaller than v6
Preserve basic structure (Processes, files, pipes. etc.)
Runs on multicores
Got paging in 2011 
To understand it, you’ll need to reads it’s source code
It’s not that hard
Textbook/commentary: xv6: a simple, Unix-like teaching operating system
Online:
Machine emulator

6. Why xv6? Why study an old OS instead of Linux, Solaris, or Windows?
1: Big enough
To illustrate basic OS design & implementation
2: Small enough
To be (relatively) easily understandable
3: Similar enough
To modern Oses
Once you’ve explored xv6, you will find your way insde kernels such as Linux

7. XV6 Structure Monolithic kernel Provides services to running programs
Processes uses system calls to access system services
When a process call a system call
Execution will enter the the kernel space
Perform the service
Return to the user space

8. XV6 system calls

9. XV6 system calls (2)