1. Exam Review cs550 Operating Systems

2. Preliminary Information Exam will focus on new content, but old content is still fair game. Exam format will be the same and of similar length to the previous exams. Remember, if you score better on this exam than you did on one of the previous exams, the final exam score will replace the worse of those two scores. We have built upon much of our old content in getting to the new content.

3. Overview Topics covered in this class included: – UNIX/Linux command line tools – C programming – MPI and POSIX (pthreads) Threads Libraries for C – Processes and Threads – Synchronization – Deadlock – Scheduling – File Systems – Memory Management – Cache and Cache Coherency – IO Systems – Protection and Security (briefly)

4. Processes and Threads Understand and be able to describe the Ready, Run and Blocked States. Understand the definitions of processes and threads and how they may be represented programmatically (pthreads and MPI). Be able to write programs that make use of threads and processes. Be able to describe and recognize synchronization errors such as race conditions and fix them.

5. Synchronization Be able to understand, describe, and use synchronization primitives. – Semaphores – Mutex Locks and Condition Variables – Atomic Variables Be able to write and describe pseudocode for the following example of synchronization – Readers/Writers Problem – Producer-Consumer Problem

6. Implementations of Processes and Threads Be able to write MPI code using the following primitives – Rank (Process Id) – Size (Number of processes) – Blocking Send and Receive – Non-Blocking Send and Receive – Barriers Be able to write threaded code and make use of synchronization primitives – Know how to create, join, and terminate threads – Know how to make use of shared variables

7. CPU Scheduling Know scheduling policies – FCFS – First Come First Served – SJF – Shortest Job First – SRTN – Shortest Remaining Time Next – RR – Round Robin Know that others exist too (Dynamic/RT scheduling) Know about CPU Bursts, Time Slices, and how the Scheduler works with the Ready and Run States

8. Know parts of Scheduler Know parts of scheduler – Dispatcher – Context Switcher – Enqueuer Know preemptive vs. non-preemptive Know Gantt charts and scheduling performance Know about multilevel queues and multiple processor scheduling

9. Synchronization Concepts – Mutual Exclusion – Critical sections – Race conditions – Semaphores – Mutex Locks and Condition Variables – Interprocess communication – Atomic Transaction and Monitors Implementations (Know pseudocode for these!) – Producers Consumers with Semaphores – Readers Writers with Semaphores

10. Deadlock Know how to draw a resource allocation graph. – Be sure to label multiple requests for the same resource on the exam. Know the conditions for deadlock – Circular wait – Hold and wait – Mutual Exclusion – No preemption Know the Dining Philosphers example of deadlock and at least one programmatic way to fix it by preventing deadlock.

11. Handling Deadlock Prevention – ensure Deadlock does not exist by removing one of the four conditions for deadlock. Avoidance – Utilize the Banker's algorithm to ensure a safe state exists before allowing processes to proceed. Detect and Recover – Allow deadlock to occur, but use a heuristic or algorithm to detect it, then if a deadlock has occurred, then use a graph algorithm to determine which processes are in a circular wait, and rollback to a safe state. Ignore Deadlock – Ignore deadlock and require the user or system administrator to either kill off processes or reset the system.

12. File Systems and Management Know the definition of a file and a directory and understand file permissions Understand file I/O primitives - read, write, open, close Understand file file pointers and the use of standard in/out Fragmentation and free space management Understand the difference between various types of file systems – FAT/FAT32 (Non-journaling) – NTFS (Journaling, Windows-based) – Ext4 (Journaling, Linux-based) – Lustre – a parallel file system for linux that makes use of metadata storage, object storage servers, and object storage targets Understand file system mounting and unmounting Understand the importance of DMA (Direct Memory Access)

13. Disk Drives and Management Disk drive parts – Platter, arm, spindle, head, tracks, sectors, blocks Disk I/O Scheduling – FCFS – Shortest Seek Time First (SSTF) – Elevator (SCAN) – Circular Scan

14. Cache Understand the importance of cache Understand Cache-Coherent Non-Uniform Memory Access Understand cache coherence methodologies – Snooping – Snarfing Understand the importance of cache misses with respect to paging and thrashing

15. Memory Management Partitions Contiguous vs Non-contiguous allocation – Frames – Pages – Segments – Fragmentation Process address space Swapping memory Virtual Memory Understand the Translation Lookaside Buffer

16. Paged Memory Paging policy – Fetch – Demand – Prepaging Replacement Policies – LRU – FIFO – Optimal

17. I/O Systems I/O Hardware and Buses (e.g. PCI and Daisy Chaining) I/O Ports, Polling, and Algorithm for Data Transfer Interrupts and Interrupt Requests Direct Memory Access Blocking and Non-blocking I/O Asycnhronous System Calls Spooling Kernel Data Structures – Know the definition of an iNode (See I/O Systems notes)

18. Security and Protection (Chpt 14) Know that protection is an internal OS problem and that there are various mechanisms and policies for OS protection – Read about the principle of least privilege in Chpt 14 – Domains – know that these consist of both hardware and software objects – Know the definition and parts of the Access Matrix Global table Access Lists Capability Lists – Read about access control