1. Welcome to OS Class!

2. Syllabus
Meet Neighbors
Be Laid back
Ask ????

3. Chapter #1
Read up to and including 1.6

4. What is an O.S.? (Definition #1)
The kernel.
Book says kernel like a government -- decided allocation of resources.
Deciding allocations and handling concepts central to O.S.
Also provides hardware abstraction.
How to recognize the kernel
One program running all the time from boot to shutdown (the kernel).
Runs at highest processor level.
Not the "main application".

5. What is an OS (Definition #2)
The kernel plus
the standard set of utilities that come with the kernel.
Shared libraries that provide the a common set of algorithms
Provides a flavor (command line, icons, file name schemes, etc.)
Definitions is loose -- others might disagree.

6. Computer System
Hardware.
Operating software.
Applications.
Users.

7. Typical Hardware Picture

8. Hardware (For Reelz)

9. Storage Hierarchy
Remember: Volatile vs non-volatile

10. How to create the Illusion of Simultaneity

11. Multiprocessing continued
Run some process for
About 1/1,000 of a second Or
They do an I/O that makes them wait
Repeat
They all seem to be moving along
Remember, movies are at 1/24th, TV is at 1/60th
And if there is more than one core???

12. How to do I/O (step 1)
Application makes a request of the OS that needs I/O.
Read/Write/Seek/Open
Request for memory
Run a program
Lots more
Application is typically paused here.

13. How to Do I/O (step 2)
O.S. translates this into an operation of a device
Get a sector of a HD, write a network packet, etc.
O.S. gives operation to device driver
Device driver loads parameters into registers
Last load should start the device

14. How to do an I/O (Step 3a)

15. How to do an I/O (Step 3b) Wait for op to finish Run another process
Do something productive
How many CPU cycles?

16. How to do I/O (step 4) Interrupt!
A hardware signal to the OS to stop and attend the hardware sending the interrupt.
Device driver and O.S. finishes operation
Maybe copy data where it goes
Maybe process data
Restart the process

17. Dual Mode CPU starts in supervisor (monitor) mode
When an interrupt happens, go to monitor mode.
All I/O required monitor mode.
Memory access are checked to make sure you’re accessing only your stuff.
O.S. puts CPU in user mode before running any user process.

18. Vocab Review
Multitasking – Seem to do lots of things at the same time.
Dual mode – CPU has a privileged and a user mode
Interrupt – A hardware signal that alerts the CPU
Storage Hierarchy – Types of storage devices raging from cheap and capacious to fast.