1Lecture 1Introduction to Operating SystemsSeptember 25, 2003Prof. Joe PasqualeDepartment of Computer Science and EngineeringUniversity of California, San Diego© 2003 by Joseph PasqualeCSE 120: Principles of Operating Systems2Welcome to Operating Systems!Operating system: the single-most complex andessential software you run on your machineIn this class, we will explore how an OS works• Basic concepts• Structure, design, implementation• Principles that apply to all OS’sThis is my favorite class! I hope it will be yours too!3IntroductionsInstructor• Prof. Joe Pasquale• APM 5121TA’s• Jesse Steinberg• John Ehrhard• Sriram Ramabhadran• Sunny Chow4ResourcesWeb page• http://www-cse.ucsd.edu/classes/fa03/cse120/Lecture notes• Will be posted day before lectureBook• Operating System Concepts, 6th EditionSilberschatz, Galvin, GagneWiley, 20035Lectures vs. BookLectures are very important: Don’t miss them!Designed to highlight what is most important to knowExam questions will come directly from lectures• Lecture notes + what is said in classUse the book to fill in details and gaps6Grading30% Midterm40% Final30% Programming Assignments (3)• Can collaborate, but must submit your own work• Exams will include questions on programmingCollaborate: discuss problems, approaches, not solutions7How to Ace this ClassGetting the most out of lectures•Come to class with lecture notes, annotate• Afterwards, read book using notes as a guide• Prepare by reading book before classPreparing for exams• Study the notes carefully•Using notes as your guide, study bookProgramming assignments: get an early start!8What is an Operating System?Basically, software the enhances the hardwareBut what does it do? How does it help?• Helps you (as a user or programmer) by making thesystem easier to use• Helps your programs run by providing resourcesand protecting them• Helps the system by keeping things runningsmoothly9We Focus on the KernelThe kernel:• All programs depend onit to run• Operates closely withthe hardware• Allocates basic resourceslike the CPU and memory• Controls I/O devicesWhen we say “OS” we mean the kernelUser ProgramsKernelHardware10Two Goals of Operating Systems1. Manage/coordinatehardware resources sothat the systemoperates smoothly:efficiently, reliably,securely2. Present abstract systemmodel to programmerthat promotes simple andconvenient access to andcontrol of resourcesUser ProgramsKernelHardwarepresent simple system modelmanage hardware resources11Manager/Coordinator of ResourcesCoordinates who gets what• “who”: running programs• “what”: resources• “when”: scheduling time• “where”: organizing space• “whether”: limits, rightsGoal: smooth system operation• efficiency, reliability,securityUser ProgramsP1 P2KernelMemoryCPUI/O Dev I/O Dev...12Present Abstract System ModelOS provides abstractions for resources, how theyoperate and interact, and policies to manage them• “who”: processes• “what”: contexts, segments, files, sockets, etc.• “when”: deadlines, priority, round-robin, etc.• “where”: best-fit, first-fit, contiguous, etc.• “whether”: exclusive-access, read-only, etc.Goal: simple/convenient access/control of resources13What If No Operating System?All we have is bare hardwareYou want to run a program• How do you load it?• How do you run it?• What happens when itcompletes?Need at least some minimalOS to do these functionsBare HardwareUser Program14 Provides Ability to Run a ProgramMinimal kernel• resident code that runs bydefault• allows you to load memorywith program and run• when done return to kernelQuestions• What happens if programfails or has a bug?• How is kernel protected?HardwareUser ProgramMinimal Kernel15Provides Commonly Needed FunctionsSome functions needed by many programs• I/O device control,memory allocation, etc.• Place these functions inkernel, called by programsWhat should functions be?• How many programsshould benefit?• Might kernel get too big?HardwareUser ProgramKernel16Allowing Multiple Programs to RunWhen I/O request is made, CPU becomes idle• allow another programto run: multiprogramming• requires yielding (giving upCPU) and sharing memoryWhat if one running program• monopolizes CPU, memory?• reads/writes another’smemory?• uses I/O device being used by another?User ProgramsP1 P2KernelMemoryCPUI/O Dev I/O Dev...17Creating IllusionsMultiple virtual processors byrapidly switching use of CPUMultiple virtual memories bymemory partitioning andre-addressingIdealized devices by simplifyinginterfaces, and using otherresources to enhance functionBottom line: make the systemeasy to use and work wellVMUser ProgramsKernelMemoryCPUI/O Dev I/O Dev...VPVMVPP1 P218Outline of Course• Processes• Virtual Memory• I/O System• File System• Protection and Security• Distributed Systems and
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