Operating Systems Overview for Computer Science Students

1. Overview • This and the other PowerPoint files represent an outline only. Each student is responsible for additional details specified in the book or in class

2. The web site [http://www.os-book.com/] has a collection of practice problems and solutions. At the end of each chapter, you should download the exercises, write the solutions and then check them against the published solutions.

3. Chapter 1: • What is an OS? • Coordinate access to resources • Make hardware usable • Allocate resources • Schedule activities • Control flow of information among hardware components. • Traffic cop

4. What actually constitutes an OS is not that simple (see author’s comments on the second paragraph on page 6)

5. Overview of a computer system: Fig 1.2 • Machine Language instruction format (von Neumann architecture). • Fetch-analyze-execute cycle. • Fetch an instruction and store in the Instruction register • Analyze it • Execute it, if possible • Registers: general, program counter, instruction register.

6. Storage hierarchy: fig 1.4

7. Types of environments • Batch • Time-sharing • Interactive • Real-Time • Single-processor • Multiprocessor

8. Multiprocessor • Asymmetric (master-slave model) • Symmetric (processors are peers) – most common • Clustered – like multiprocessor except consists of 2 or more entire systems coupled together. Clustered may mean different things to different people.

9. Types of OS • Single tasking • Multitasking (sometimes called timesharing) • Multiuser

10. Interrupts vs. traps (exceptions). • Interrupt: Occurrence of an event that requires that the CPU be interrupted from what it is doing in order to execute an interrupt handling routine (e.g. completion of an I/O or a hardware failure) • Trap: an event typically caused by the CPU such as an attempt to divide by 0, numeric overflow, or illegal memory reference. Requires execution of a trap-handling routine.

11. Dual modes (user mode; monitor, kernel, or supervisor mode) – defined by an internal CPU bit; privileged instructions. • Process: an entity capable of requesting and using computer resources. E.g. a program in execution.

12. OS responsibilities • Process management: • Creating/deleting processes. • Process synchronization. • Interprocess Communication. • Suspending/resuming processes. • Deadlock handling:

13. Memory management: • Allocation/deallocation of memory • What processes go into memory and where • What part of memory is occupied/available. • Static/dynamic allocation

14. Caching (paging, hardware caching). • Security: protect memory from other processes.

15. Scheduling • Which processes run? • For how long? • Which have higher priority? • Are they waiting for something?

16. File management: • Create/delete files • Maintain directories • Storing files on secondary storage • File access • File security • Manage disk space (auxiliary storeage management)

17. Goals • Consistency • Scalability • Ease of use • Efficiency • Throughput • Responsiveness

18. Above goals are often contradictory. Ease of use often implies guis which are NOT efficient. Linux is known to be stable and efficient, but not easy to use. • Best throughput may be obtained by ignoring certain activities, which means bad response times for them.

19. Examples • DOS • Various windows flavors • Various Unix flavors • VMS • MVS • Mac

20. Distributed systems: collection of processors, each with its own local memory, connected by high-speed lines. • Embedded systems: Most common – embedded in consumer devices (cars, DVDs, robotic arms, cell phones, ipods, etc)

21. Client-server computing • Peer-to-peer computing. • Can skip this stuff.

22. Chapter 2: • Shell/command interpreter. Commands are really files (e.g. ls, rm, cat, etc.) • Interface: command line or gui. • Linux flavors have various shells: Bourne shell, C shell, Korn shell. They look alike but there are small differences. • We use the 2nd version of the Bourne shell. It’s called bash (Bourne Again Shell).

23. System Calls: interface to service made available by the OS • API (Application programmer interface): set of functions available to the programmer. • Examples: fopen, read, write, close, fork, wait, exec, etc. • Linux command handout has those we will use in this class.

24. Types of calls: fig 2.5 • Can skip most of the stuff on system calls – not needed for this stage of the course

25. OS structure • Simple structure: eg - DOS allowed programs to access routines that write directly to display and drives. Vulnerable to crashes. Fig 2.10 • Kernel: most critical components; like to keep resident in memory • Layered design: Fig 2.11 and 2.12 • Basic design principle to insulate the needs of a layer from the details of the next lowest layer

26. Microkernel: • As systems evolved, kernels grew larger. • Removes all nonessential components from the kernel and implements as system or user level programs. • Not always consensus on everything kernel should contain.

27. Linux and Mac OS use a modular kernel. See example in Fig. 2.13 • Windows XP is a layered system of modules (Figure 22.1)

28. Virtual machine: • Abstraction of hardware components. • Illusion of having your own machine. • Can be useful for testing OS changes/enhancements. • More secure (each application runs on it's own "machine") • IBM's VM operating system. • Server virtualization.

29. Java – more than just a language • Language spec - the stuff you learned • API – support for graphics, I/O, database connectivity, networking, server apps, support for telephones, pagers, etc. • Virtual machine spec. Java Virtual Machine (JVM) – Fig 2.17