1. 4061 Session 27 (4/23)

2. Today Virtual Machines and Emulation

3. Today’s Objectives Understand some of the challenges and applications of virtual machines

4. Admin My office hours on Wednesday cancelled HW 5: Due day of final Quiz 5: Last day of class

5. What is a virtual machine? What are some examples of virtual machines?

6. Virtual Machines One machine == one OS? –What about One machine, many OS Many machines, one OS Portability of code –Why are Java and Python more portable than C? Virtual machines are a new layer of abstraction

7. Why not 2? Why not run two operating systems at the same time on one box?

8. VM History 1972, IBM System/360 Mainframes –Isolation between users –Era before user/kernel mode bit Little activity in 80s and early 90s Exciting area today

9. Jails “chroot jail” –Change the root directory of the calling process –Once a running process executes chroot("/home/jail"), /home/jail becomes "/“ –Can no longer access files above the new root directory Jail is enforced by the OS, not the application But applications may expect the presence of “/bin/ls”, a scratch dir, devices, and shared libs

10. FreeBSD Jail Where chroot jail was weak partitioning, FreeBSD jail is strong partitioning –Create virtual machines. Popularly used in ISPs.

11. Virtual OS on the Desktop VMWare, Parallels, KVM, Xen Different approaches –Hardware emulation –Native virtualization (with hardware) –Paravirtualization

13. Mame

14. Wine

15. Java Bytecode JVM: JIT compiling Advantages –Portability –Security

16. Grid Computing Enable the virtualization of distributed computing resources to create a single system image across heterogeneous, geographically dispersed IT environments.