1. IS310 Hardware & Network Infrastructure Ronny L
IS310 Hardware & Network Infrastructure Ronny L. Bull, MS Lecturer Computer Science Department

2. Today's Lecture Topics Processes Resource Sharing Deadlock
Dining Philosophers
OS Security

3. Processes Process: the activity of executing a program
Process State: Current status of the activity
Program counter
General purpose registers
Related portion of main memory
Ready: a process is ready if it is within a state in which it can continue
Waiting: a process is waiting if the process is delayed until some event occurs
Resource allocation

4. Process Administration
Scheduler:
adds new processes to the process table
removes completed processes from the process table.
Process Table: an area in main memory maintained by the process scheduler.
Dispatcher: controls the allocation of time slices to the processes in the process table
The end of a time slice is signaled by an interrupt

5. Process Time Sharing
Multiprogramming: dividing processor time into short segments (Time Slices) measured in either milliseconds or microseconds
Context Switching: the procedure of changing from one process to another

6. Interrupts
Interrupt: a signal that “interrupts” the CPU from its current task
CPU completes its current machine cycle
Process state is recorded
Starts interrupt handler
Interrupt handler:
Located in a predetermined location in main memory
Describes how dispatcher should respond to the interrupt signal

7. Process Time Sharing

8. Handling Competition for Resources

9. Handling Competition for Resources
Semaphore: a “control flag”
Critical Region: a group of instructions that should be executed by only one process at a time
Bank account example
Mutual exclusion: Requirement for proper implementation of a critical region
Mutex

10. Deadlock

11. Deadlock Processes block each other from continuing
Conditions required for deadlock (all three must be satisfied)
Competition for non-sharable resources
Resource requested on a partial basis
An allocated resource can not be forcibly retrieved

14. Security
What kind of concerns should we have when it comes to operating system security?
What are some ways that can be used to tighten up security on within an operating system
What are privilege levels? Privileged instructions?