Operating Systems

1. OperatingSystems CIS 432 David Goldschmidt, Ph.D. Computer Science The College of Saint Rose

2. What is an Operating System? • An Operating System is the software interface between hardware and its users(via application software) • Operating systems: • Execute user and system programs • Manage & coordinate computer hardware • Serve as resource allocators • Are typically interrupt-driven

3. Operating Systems • System Software • Computer programs that directlycontrol the operations of thecomputer and its devices • Operating System • Coordinates and orchestrates all activitiesof the hardware devices in a computer • Provides a Graphical User Interface (GUI) forusers to interact with the computer

4. Design Goals of an Operating System • From a user’s perspective, an operating system should be: • easy to use • easy to learn • reliable • safe • fast • System goals ofan operating system typically include: • reliability • flexibility • extensibility • speed • efficiency • maintainability

5. Functional Components • Functional components of anoperating system include: • Process manager • Memory manager • Virtual memory manager • File manager • Device manager

6. History of Operating Systems • In the beginning… …the 1940s ENIAC

7. computerprograminside History of Operating Systems • Automation in the 1950s using punch cards

8. Batch Jobs • A job is a unit of work submitted by a user tothe operating system, typically consisting of: • a program either in a sourcelanguage or in binary form • a set of input data used bythe program when it executes

9. History of Operating Systems • IBM 360 introduced… …in 1964

10. Multiprogramming

11. Multiprogramming • In multiprogramming, several jobs reside in memory simultaneously • CPU use is sharedand managed by theoperating system

12. Multiprogramming • Multiprogramming provides efficient use of the computer (CPU) and its resources (e.g. I/O) • One user cannot keep theCPU and I/O devices busyat all times • Each running program iscalled a job • Multiprogramming organizesjobs such that the CPU alwayshas exactly one to execute

13. Multiprogramming • Computer is often idle – why? • CPU and hardware muchfaster than I/O • When a user or process isblocked waiting for I/O,the operating system switchesto another job • A subset of jobs is storedin memory, awaiting CPUor other resources

14. Timesharing (Multitasking) • To ensure fairness, consider a timesharing scheme in which the CPU cycles through all jobs • Each job (process) is givena fixed amount of CPU time • Switching from one runningprocess to another is calleda context switch • A process may relinquish itstime if blocked on an I/O request

15. Timesharing (Multitasking) • Unless blocked on I/O, processes line up,awaiting their turn with the CPU • CPU scheduling algorithmis necessary to efficientlydecide the order in whichprocesses execute • If processes do not fit intomemory, the operating systemwill swap them in and out ofmemory from virtual memory

16. and the Apple IIe History of Operating Systems • Personal computer revolution… …of the late 1970s and early 1980s

17. History of Operating Systems

18. History of Operating Systems • World Wide Web and Internet revolution… …of the 1990s and 2000s

19. …and networked system bus Computer System Organization • Computer systems are increasingly complex • Require an operating system to coordinate and control hardware activities

20. Computer Networks • A Local Area Network (LAN) is a networkof machines coveringa limited geographicalarea • A Metropolitan AreaNetwork (MAN)covers more denselypopulated area

21. Computer Networks • A Wide Area Network(WAN) covers multiplelocations • Each location consistsof one or moreLANs or MANs

22. Computer Networks • LANs connect to other networks via a router

23. Central Processing Unit (CPU) • Software instructions are executed bya Central Processing Unit (CPU) • An external hardware event triggersan interrupt by signaling the CPU • e.g. mouse movement, keyboard event • Software triggers an interrupt byexecuting a system call • e.g. disk read, graphics output, printer output

24. Interrupt Mechanism • Interrupts are handled much like calling a function or method in a programming language I/O devicestypically use abuffering strategy

25. interrupt processing times vary… …as do I/O transfer times Typical Interrupt Timeline

26. Synchronous & Asynchronous I/O Synchronous Asynchronous

27. very fast very small volatile very slow very large Hierarchical Storage Architecture non-volatile

28. why implement caching in an operating system? What is Caching? • Caching is a technique totemporarily store data ina smaller and fastermemory component

29. Performance • A key goal in operating system design isachieving fast and efficient performance

30. Retrieving Data from a Cache • When the operating system attempts to read from memory, check to see if the requested data is already in the cache • If it is, data is read from the cache (fast!) • If not, data is copied from memory to the cache (maybe next time…)

31. memory location X Principle of Locality • When a running program reads from memory location X, the principle of locality predicts that the next memory location requested will be near X • Store pages of data in a cache, where each page is typically the same size (e.g. 16KB)