Process Management

Question 1

What is Multitasking?

Answer 1

Two or more programs active with interleaved execution

Question 2

What is Multiprocessing?

Answer 2

A computing environment with multiple processors

Question 3

What is a Program?

Answer 3

A series of instructions (static)

Question 4

What is a Process?

Answer 4

• A program with its execution state (dynamic)
• You can have many processes all executing the same
  program with different state

Question 5

Outline the life of a process.

Answer 5

• Process is created
• Cycles between CPU bursts and I/O bursts
• Process ends

Question 6

What is the 5 State model?

Answer 6

New:
- The OS is creating the PCB and allocating initial resources to the process
Ready:
- The process is waiting for its turn to use the CPU
Running:
- The process is running on the CPU
Blocked:
- The process is waiting for some event to happen
(I/O, timer, child to end, interrupt)
Exiting:
- The OS is reclaiming the process’ resources and notifying its parents

Question 7

What are the 2 kinds of scheduling?

Answer 7

Nonpreemptive and Preemptive

Question 8

What is Preemptive scheduling?

Answer 8

-  The OS decides when a process has had enough CPU time
-  Packages up the state of the process and moves the process to the
ready queue
-  The transition is undetectable to the process

Question 9

What is Nonpreemptive scheduling?

Answer 9

-  The process decides when its computations are in a stable state to
give up the CPU ( Eg. System call )
- Uncommon today

Question 10

What is a context switch?

Answer 10

The event of saving the state of a process in the
running state to its PCB and of restoring the state of
another process from its PCB to the hardware.

Implications:

• Empty hardware caches
• Flush instruction pipelines
• Stop all look-ahead processing

Question 11

Common Schedulers

Answer 11

Short term scheduler:

• Determines who will execute next – orders the ready queue
• Executed frequently

Long term scheduler:

• Determines when a process can transition from new to ready
• Tries to ensure a good mix if CPU-bound and I/O-bound processes

Question 12

Less Common Schedulers

Answer 12

Dispatcher:
- The code that actually does context switches
- If no dispatcher then the short term scheduler does the context switch
Medium term scheduler:
- Monitors the performance of the system and can temporarily
remove processes from the ready queue and/or adjust resources
seen by the long term scheduler to ensure good system
performance