1. Operating systems design philosophy ESMAIL ASYABI- FEBRUARY 2015

2. What is Operating systems  Extended virtual machine  Resource manager

3. OS as a extended virtual machine  Accessing the hardware directly could be very complex ◦kernels implement a set of hardware abstractions. ◦They hide the complexity, ◦They provide a clean and uniform interface to the underlying hardware.

4. Kernel Types  Kernels can be classified into three broad categories ◦ Monolithic kernels ◦Micro kernel ◦Hybrid Kernel (This is bit controversial. We will see why it is )

5. Monolithic kernels Example : MS-DOS, BSD, HP-UX, AIX, Windows 98

6. Microkernel

7.  It moves parts of the kernel away from the dangerous kernel space into userspace  limit the amount of damage a bug can cause.  the parts run in isolated processes (so-called ‘servers’) as a consequence, they do not influence each other’s functioning.  If a subsystem will crash (e.g. networking server), all other subsystems will continue to function.  microkernel operating systems have a system in place which will automatically reload crashed servers.  Mach, Minix, QNX, L4

8. Hybrid Kernel Microsoft Windows NT, 2000, XP, Vista, and 7. Apple Mac OS X uses a hybrid kernel

9. Less Is More (XEN) Xen attempts to do less than the previous version. The reason for this is that Xen runs at a very high level of privilege above even the operating system. A bug in a program may compromise the data that that program can access, a bug in a kernel might compromise an entire system, but a bug in Xen can compromise every virtual machine running on a machine. For this reason, it is important that the Xen code be as secure and bug-free as possible.

10. OS as a resource manager  FCFS  RR  SJF

11. Fairness

12. Fairness (equality)  Equality simply means that two things are judged to have the same value.  Judging two people as having the same value before the law (i.E. Equal protection) is an objectively good thing.  Judging that any two people have the exact same needs is objectively wrong though.  Equality might be good in some things, but its opposite- individuality also has its own uses and benefits.

13. Fairness vs sameness

14. Sameness In the OS  For example in process scheduling P3 P2 P1 P2 P3

15. Fairness (equity)  the quality of being fair P3P1 P2 P1 P2 P3

16. Fairness (Sameness VS Equity)

17. QoS Aware Operating Systems (clouds)