Introduction Topics What s an operating system? Course policy

Transcription

1 CENG334 Introduction to Operating Systems Introduction Topics What s an operating system? Course policy Erol Sahin Dept of Computer Eng. Middle East Technical University Ankara, TURKEY URL: Some of the following slides are adapted from Matt Welsh, Harvard Univ. Week 1 18/02/08 1 Welcome to CENG334! What is this course about? Operating Systems drive the inner workings of virtually every computer in the world today PCs, servers, ipods, cell phones, missile guidance systems, etc. all have an OS that dictate how they operate. The OS manages many aspects of how programs run, and how they interact with hardware and the outside world. 2 1

2 3 Welcome to CS161! What is this course about? Operating Systems drive the inner workings of virtually every computer in the world today PCs, servers, ipods, cell phones, missile guidance systems, etc. all have an OS that dictate how they operate. The OS manages many aspects of how programs run, and how they interact with hardware and the outside world. Understanding the OS is essential for understanding: System performance and reliability Resource management Virtualization and abstraction Concurrency and parallelism Hardware interfaces and I/O This course is about more than just kernel internals It is really about learning complex systems design. 4 2

3 What is an operating system? Software that provides an elaborate illusion to applications User application User application User application Protection boundary Kernel Memory management Process management Accounting Filesystem TCP/IP stack Device drivers Disk I/O CPU support Hardware/software interface Gnarly world of hardware 5 One OS Function: Concurrency Give every application the illusion of having its own CPU! I think I have my own CPU So do I! 6 3

4 One OS Function: Concurrency The OS timeslices each application on a single CPU Switches between applications extremely rapidly, i.e., 100 times/sec Kernel Scheduler Timeslice on single CPU system time 7 Another OS Function: Virtual Memory Give every application the illusion of having infinite memory And, that it can access any memory address it likes! In reality, RAM is split across multiple applications Physical RAM Code Data Stack VM System Code Data Stack Swap out to disk 8 4

5 Multiprocessor support Modern systems have multiple CPUs More OS Functions Can run multiple applications (or threads within applications) in parallel OS must ensure that memory and cache contents are consistent across CPUs Filesystems Real disks have a hairy, sector-based access model User applications see flat files arranged in a hierarchical namespace Network protocols Network interface hardware operates on the level of unreliable packets User apps see a (potentially reliable) byte-stream socket Security and protection Prevent multiple apps from interfering with each other and with normal system operation 9 Why bother with an OS? Not just to give Slashdot readers something to argue about... What do you think? 10 5

6 Why bother with an OS? Not just to give Slashdot readers something to argue about... Abstract away messy details of hardware Give apps a nice clean view of the system Save programmers a lot of trouble when building applications Allow apps to be ported across a wide range of hardware platforms Safety! Don't let applications run amok keep them in a sandbox e.g., Access to unallocated memory address crashes only the program, not the whole system Segmentation fault core dumped Efficiency Share one machine across many different apps: concurrent execution You would be surprised how much slack there is in a typical computer system 11 Why study operating systems? Most people will never write one from scratch... ( rich (Though if you do you stand to get incredibly ( BSD Although more and more people are hacking them (e.g., Linux and You need to understand the big picture in order to hack the details This class is about much more than the kernel! Data structures, concurrency, performance, resource management, synchronization, networks, distributed systems, databases... The ideas and skills you pick up in this class have broad applications And it doesn't hurt for those Microsoft interviews either This course is the basis for future work in other areas of systems Distributed systems, P2P, sensor nets, etc. 12 6

7 Structure Major OS Design Issues How is the OS itself organized? Lots of modules? One big blob of code? Sharing How are limited resources multiplexed across users? Naming How to programs and users name and access resources? Security How to prevent malicious users from compromising the system? Performance How to keep it all fast? Reliability What happens when a program (or the OS itself) has a bug or failure? 13 Extensibility More OS Design Issues How do users and developers add new features? Communication How do programs exchange information? Concurrency How are multiple concurrent activities created and controlled? Scale What happens when demands on resources increase? Distribution How do many computers interact with each other, e.g., to pool resources? Accounting How do you track (and maybe charge for) resource usage? 14 7

8 There was no OS just libraries In the Beginning... Computer only ran one program at a time, so no need for an OS And then there were batch systems Programs printed on stacks of punchhole cards OS was resident in a portion of machine memory When previous program was finished, OS loaded next program to run Disk spooling Disks were much faster than punchcards read stack onto disk while previous program is running With multiple programs on disk, need to decide which to run next! (! disk But, CPU still idle while program accesses a peripheral (e.g., tape or Harvard Mark I, 1944 ENIAC, 1945 IBM 360, 1960's 15 Multiprogramming To increase system utilization, multiprogramming OS s were invented keeps multiple runnable jobs loaded in memory at once Overlaps I/O of a job with computing of another While one job waits for I/O to compile, CPU runs instructions from another job To benefit, need asynchronous I/O devices need some way to know when devices are done performing I/O Goal: optimize system throughput perhaps at the cost of response time Dennis Ritchie and Ken Thompson at a PDP11,

9 Timesharing To support interactive use, timesharing OS's were created multiple terminals connected to one machine each user has illusion of entire machine to him/herself optimize response time, perhaps at the cost of throughput Timeslicing divide CPU fairly among the users if job is truly interactive (e.g. editor), then can switch between programs and users faster than users can generate load MIT Multics (mid-1960 s) was the first large timeshared system nearly all modern OS concepts can be traced back to Multics 17 Personal Computing Totally changed the computing industry. CP/M: First personal computer OS IBM needed OS for their PCs, CP/M behind schedule Bill Gates to the rescue: Bought 86-DOS and made MS-DOS DOS is basically a subroutine library! Apple I, 1976 Apple LISA, 1983 Many popular personal computers follow Apple, Commodore, TRS-80, TI 99/4, Atari, etc... Bill Gates and Paul Allen, c.1975 IBM PC, 1981 Commodore VIC

10 19 Parallel Computing and Clusters High-end scientific apps want to use many CPUs at once Parallel processing to crunch on enormous data sets Need OS and language primitives for dividing program into parallel activities Need OS primitives for fast communication between processors degree of speedup dictated by communication/computation ratio Many kinds of parallel machines: SMPs: symmetric multiprocessors several CPUs accessing the same memory MPPs: massively parallel processors each CPU may have its own memory Clusters: connect a lot of commodity machines with a fast network 20 10

11 Distributed OS Goal Make use of geographically distributed resources workstations on a LAN servers across the Internet Supports communication between applications interprocess communication (on a single machine): message passing and shared memory networking procotols (across multiple machines): TCP/IP, Java RMI,.NET SOAP The Grid,.NET, and OGSA Idea: Seamlessly connect vast computational resources across the Internet 21 Embedded OS The rise of tiny computers everywhere ubiquitous computing Processor cost low enough to embed in many devices PDAs, cell phones, pagers,... How many CPUs are in your car? On your body right now? Gets more interesting with ubiquitous networking! Wireless networks becoming pervasive Sensor networks are an exciting new direction here Little motes with less 4KB of RAM, some sensors, and a radio Typically very constrained hardware resources slow processors very small amount of memory (e.g. 8 MB) no disk but maybe quasi-permanent storage such as EEPROM 22 11

12 Teaching staff Instructor: Section 1, 2: Dr. Erol Sahin Location: B-111, Tel: , Office hours: by appointment. Teaching assistant: Hande Celikkanat 23 Textbook Operating System Concepts Seventh Edition Avi Silberschatz Peter Baer Galvin Greg Gagne John Wiley & Sons, Inc. ISBN X Modern Operating Systems, 2/E Andrew S. Tanenbaum Prentice Hall., 2001, ISBN-10: ISBN-13: Both books should be available at the bookstore

13 Grading Midterm: 25 % [April 16] Assignments: 40 % Final: 35 % 25 Assignments ( 9% ) Assignment 1: Basic Shell process management, Unix system calls ( 9% ) Assignment 2: Basic Threading thread management and synchronization ( 9% ) Assignment 3: Virtual Memory paging algorithms, TLB handling ( 13% ) Assignment 4: File System ext2 file system implementation, inode/block concepts, file/directory handling 26 13

14 Policies Late assignments: Late submission policy will be announced for each assignment. %100 = meeting the deadline. %60 = within 1 week of the deadline. %0 Academic dishonesty: All assignments submitted should be fully your own. We have a zero tolerance policy on cheating and plagiarism. Your work will be regularly checked for such misconduct and any such attempts will be prosecuted: At all times you have the right to challenge our decisions on cheating, upon which the case will be processed through the disciplinary channels of the university. However, we would like to remind you that, if found guilty, the legal code of the universityproposes a minimum of six month expelsion from the university. 27 Cheating What is cheating? Sharing code: either by copying, retyping, looking at, or supplying a copy of a file. What is NOT cheating? Helping others use systems or tools. Helping others with high-level design issues. Helping others debug their code

15 Communication Online information about the course will be available on the CENG334 web page: Announcements about the course will be made at the CENG334 newsgroup at news://metu.ceng.course.334 Please put Section 1,2 on the subject line of your posting. If you have a specific question you can send an to the us. However make sure that the subject line starts with CENG334 [capital letters, and no spaces] to get faster reply