1. Scheduling & File Management
Operating Systems
Scheduling
&
File Management
1) These notes are © Aiman Hanna. All copyrights reserved. For more information please to:
2) These notes are also based on: Operating Systems, 3rd edition by Garry Nutts, published by Addison Wesley, ISBN-10: | ISBN-13: These notes still totally enforce all copyrights for Nutts/ Addison Wesley. For more information on these rights, please refer to the original publication of the book.
3) VERY IMPORTANT: These notes are neither complete nor sufficient to study for the course. They are merely given so that you can follow the covered subjects. You should NEVER depend solely on these notes for your study.
Any use of these notes that results in violation of any of the copyrights indicated above is strictly prohibited.
© Prof. Aiman Hanna
Department of Computer Science Concordia University Montreal, Canada
Data Communications & Computer Networking, by: Aiman Hanna

2. Preemptive Strategies
SJN
Priority
Deadline
Round Robin (RR)

3. Issues with RR Number of Context Switches
RR with overhead must then be considered
Priority issues with RR; how can priority be implemented?

4. Multiple-level Queues
Needed to achieve priority
However, how can priority be achieved, yet starvation be avoided?
Multiple-level queues with and without feedback

5. File Management Why files, in particular, need an OS manager
File descriptors
Low-level vs. high-level file systems

6. Allocation Strategies for File Blocks
Contiguous strategy
Linked List strategy
Doubly Linked List strategy
Indexed (Index Table) strategy
Advantages and disadvantages of each of these strategies

7. Allocation Strategies for File Blocks
Unix File Structure
Why is it too good?
Examples of this allocation strategy were discussed in class

8. Strategies for Tracking Unallocated Blocks
Linked List
Bit Map

9. Where is this week coverage in the textbook?
Chapter 7:
Section 7.5
Note: Much details were provided in class for multiple-level Queues. You must refer to your class notes for these details.
Skip: Section 7.6
See next slide for textbook coverage of File Management

10. Where is this week coverage in the textbook?
Chapter 13:
Sections 13.2 and 13.3, with the following exceptions:
 Skip:
Figure 13.2 page 517
Figure page 524
Figure 13.7 page 525
Indexed Sequential Files (page 525) until the end of this section, section 13.2 (page 528)
Unix open and close (page 532 to 534)
The DOS FAT file system (page 539 to 540)
Reading and Writing the byte stream (page 541 to 544)
Skip: Sections 13.1, 13.4, 13.5, 13.6 & 13.7