Operating System Organization

1. Operating System Organization Chapter 3Michelle Grieco

2. Outline • Basic Functions of an OS • Defining Requirements • Implementation Considerations • OS Kernels of Today • Research in OS

3. Purpose of an OS • Creates abstractions • Multiple processes compete for use of processor • Coordination

4. Responsibilities of an OS • Create an abstract machine environment with multiple, autonomous, abstract components (that can be in use concurrently) • Multiprogramming is used to create an abstract machine for each process • Coordinate the use of the components according to the policies of the machine’s administrator • Scheduler decides when and which processes get to use the processor

5. Basic Requirements an OS Must Satisfy • Device Management • Process, Thread and Resource Management • Memory Management • File Management

6. Device Management • OS manages the allocation, isolation and sharing of devices according to policies chosen by the designer or system administrator. • Devices treated in a general manner • Special approaches for memory and processor

7. Device Management Device-Independent Part Device-Dependent Part Device-Dependent Part Device-Dependent Part Device Device Device

8. Process, Thread and Resource Management • Basic units of computation • Elements of the computing environment needed by a process so that its threads can execute.

9. Process Management • Unix Style • Includes management facilities to create, destroy, block, and run a process. • Thread Based Approach • More complicated since it has to manage processes and threads as separate entities

10. Resource Manager • Allocates resources to processes • Handles requests for resources from threads • Changes in status/changes in resource needs

11. Memory Management • Cooperates with process manager to allocate primary memory (executable or main) to each process • Enforces isolation, methods to allow sharing of blocks of memory • Virtual Memory – allows processes to reference information stored on a storage device as if it were stored in primary memory.

12. Memory Management Memory Manager Isolation and Sharing Virtual Memory Block Allocation Process Manager Storage Devices Primary Memory

13. File Management • Why do we need a file manager? • Provides an abstraction layer • Distribution of information across networks

14. OS Implementation Considerations & Mechanisms • Considerations • Performance • Exclusive Use of Resources • Mechanisms • Processor Modes • Kernels • Methods of Invoking Service

15. Performance • OS provides simplified programming interfaces • Manage resource allocation & sharing • OS designers need to keep in mind… What is the cost? Efficiency vs. Convenience • How much do these abstractions slow down the execution of a program? • What is the performance cost of using files rather than commands to directly manipulate storage devices? • How much contribution to functionality of the system is derived versus the impact to performance?

16. Exclusive Use of Resources • Multiprogrammed systems support multiple processes and threads that need to share resources. • Design Principles: • Do not to interfere with other processes • Cannot use a resource unless it is specifically authorized to • Allow both exclusive control to a process / or shared among a set of processes

17. Exclusive Use of Resources • Implementation of Design Principles includes: • Protection Mechanisms via security policies • Defines strategies for managing resources • File Protection Policy Example • If OS enforces a policy, how do we prevent application software from overriding this policy? • Trusted vs. Untrusted software and access barriers • The kernel of the OS is trusted software • All other software is untrusted

18. Processor Modes • The key hardware element for implementation of trusted software • Mode Bit (supervisor or user) • Supervisor (privileged, protected) • Processor can execute every instruction • User • Processor can execute only a subset of all instructions

19. Kernels • What is a kernel? • Design Decisions for what goes into the kernel? • Everything but the kitchen sink? • If it is in the kernel, it will have access to other parts of the kernel. • If it is executed in user mode, it won’t have access to kernel data structures.

20. Requesting Services from the OS • Techniques to request service • System Call • User invokes a trap instruction • Message Passing • User constructs a message that requests service

21. System Call • User invokes trap instruction when application calls stub program (uses reference to trap table) • Processor is switched to supervisor mode • Branches through trap table • Executes function to be invoked • OS finishes work and returns to user mode and returns control to user process. Call (…); trap return (…);

22. Message Passing • Message constructed that requests service (message A) • OS send() system call passes the message to trusted OS process (kernel). • Executes trap • Kernel executes function while user waits for result of service request. (message receive A) • Kernel completes request it sends message B back to user process (send and receive B). send (…, A, …);receive (…, B, …); send/receive receive (…, A, …);send (…, B, …);

23. Logical Organization of OS Process, Thread and Resource Manager File Manager Memory Manager Device Manager Processor(s) Main Memory Device(s)

24. Kernels of Today • UNIX • Windows NT

25. UNIX • Goals • Implement process, memory, file and device management in the kernel but only with minimal functionality to support a broad range of policies (bare essentials to read and write byte streams) • Wanted to keep kernel as small as possible to improve efficiency • Tailored further by use of application domains and application software to solve problems • Result • Very large software module including all managers (process, memory, file and device) • Separate device drivers from kernel • Evolved from swapping systems to paging • Processing now addresses multiprocessor and distributed hardware configurations • Implementations are difficult to modify • IEEE POSIX.1 open systems standard • No cost implementation LINUX

26. WINDOWS • Goals • Extensible • Portable • Reliable • Secure

27. Summary • Value of functionality built into the OS must justify the performance cost • Modern OS includes managers for processes and resources including managers for memory, files, and devices • Implementation techniques include: the mode bit (supervisor/user) to ensure exclusive use of resources and to operate as trusted, system call interfaces and message passing mechanisms

28. Research • Here are some sites of interest on new and innovative advances in Operating Systems: • http://tunes.org/Review/OSes.html • http://www.palmsource.com/palmos/ PalmOS Cobalt 6.1 is the next generation of Palm OS. It will enable the creation of new categories of devices for the communications, enterprise, education and entertainment markets. Palm OS Cobalt 6.1 provides integrated telephony features, support for WiFi and Bluetooth, and enhancements to the user interface. • http://www.pdos.lcs.mit.edu/exo.html MIT’s AEGIS – no runtime kernel, extreme performance gain • http://www.cs.utah.edu/flux/ Flux Project at University of Utah – build your own OS using OS bricks (an OS toolkit) • http://srg.cs.uiuc.edu/2k/2K (formerly known as SPINE) is a distributed, reflective, component-based, adaptable operating system being built by researchers at the Systems Software Research Group from the University of Illinois at Urbana-Champaign and the Systems and Communications Group from the Universidad Carlos III - Madrid. • http://www.acm.uiuc.edu/sigops/roll_your_own/ write your own OS

29. Questions • You should be able to answer the following questions about this chapter: • 1. What is multiprogramming? • 2. What are the four main managers in an OS and how do they interact? • 3. What are the benefits to having an independent and dependent part of the device manager? • 4. What is a process? What is a thread? • 5. What are important considerations of a process manager? • 6. What is virtual memory? • 7. Why do we need a file manager? How is it useful? • 8. What are OS implementation considerations? What are the mechanisms we can use to implement these considerations? • 9. If OS enforces a policy, how do we prevent application software from overriding this policy? • 10. What are the two techniques to request service? How do they work?

30. Sources • Nutt, G. Operating Systems, 3rd Edition. Addison Wesley. 2004 • http://tunes.org/Review/OSes.html • http://www.palmsource.com/palmos • http://www.pdos.lcs.mit.edu/exo.html • http://www.cs.utah.edu/flux/ • http://srg.cs.uiuc.edu/2k/ • http://www.acm.uiuc.edu/sigops/roll_your_own/