Intro LectureI. Administrative MattersII. The UNIX Time-Sharing System1Lecture 1Advanced Topics in Computer Systems, CS262aProf. BrewerIntro LectureI. Administrative MattersInstructors: Eric Brewer and Joe Hellerstien Eric Brewero PhD MIT, 1994o Internet Systems, Mobile computing, Security, Parallel computingo Founded Inktomi, Federal Search Foundationo Contact: [email protected] Hellerstieno PhD, Wisconsin, 1995o Databases, declarative networkingo Contact: [email protected] prerequisite: no entrance exam this year, but please review undergrad materialTraditional goals of the course:o Introduce a variety of current OS research topicso Teach you how to do OS researchNew goals:o Common foundation for OS and database researcho Motivation: OS and DB communities historically separate, despite much overlap ingoals and ideas. We often use independent vocabulary and have largely separate“classic” papers that the other community typically hasn’t read (especially OS peoplenot reading DB papers, since a DB is “just an application”)o Part 1 of a year-long advanced systems courseo 262A satifies software breadth requirement by itselfResearch = analysis & synthesiso Analysis: understanding others’ work - both what’s good AND what’s bad.o Systems research isn’t cut-and-dried: few “provably correct” answers.o Synthesis: finding new ways to advance the state of the art.Lecture 122 parts to course:o literature surveyo term projectWill not cover basic material.Analysis: literature survey: read, analyze, criticize papers.o All research projects fail in some way. o Successful projects: got some interesting results anyway.In class: lecture format with discussionSynthesis: do a small piece of real research.o Suggested projects handed out in 3-4 weekso Teams of 2-3o Poster session and “conference paper” at the end of the semestero Usually best papers make it into a real conference (with extra work)Class preparation:o Reading papers is hard, esp. at first.o Read before class.Homework: brief summary/papero 1/2 page or lesso 2 most important things in papero 1 major flawCourse topics: (much of systems design is about sharing)o File systemso Virtual memoryo Concurrency, scheduling, synchronizationo Communicationo Multiprocessorso Distributed Systemso Transactions, recovery, & fault-tolerance3Lecture 1o Protection & securityo OS structureo “Revealed truth” — overall principlesGrad class ⇒ material may be controversial (hopefully!)Lecture format: cover 1-2 papers plus announcementsGrading: 50% project paper, 15% project demo, 25% midterm, 10% paper summarieso can miss 3 summaries without penalty, no reason needed or wantedo Summaries: < 1/2 page, at least one criticism, summary should be at most halfReading list:o No textbooko Almost everything is online, otherwise I’ll distribute copies in class. o “Warm up” paper: “UNIX timesharing” o Reading for next time: System R paper (in the Red Book)II. The UNIX Time-Sharing System“Warm-up” paper. Material should mostly be a review.Classic system and paper: described almost entirely in 10 pages.Key idea: elegant combination of a few concepts that fit together well.System features:o time-sharing systemo hierarchical file systemo device-independent I/Oo shell-based, tty user interfaceo filter-based, record-less processing paradigmVersion 3 Unix:o ran on PDP-11’so < 50 KBo 2 man-years to writeo written in CLecture 14File System:o ordinary files (uninterpreted)o directories (protected ordinary files)o special files (I/O)Directories:o root directoryo path nameso rooted treeo current working directoryo back link to parento multiple links to ordinary filesSpecial files:o uniform I/O modelo uniform naming and protection modelRemovable file systems:o tree-structuredo mount’ed on an ordinary fileProtection:o user-world, RWX bitso set-user-id bito super user is just special user idUniform I/O model:o open, close, read, write, seeko other system callso bytes, no recordsFile system implementation:o table of i-nodeso path name scanning5Lecture 1o mount tableo buffered datao write-behindI-node table:o short, unique name that points at file info.o allows simple & efficient fscko can’t handle accounting issuesProcesses and images:o text, data & stack segmentso process swappingo pid = fork()o pipeso exec(file, arg1, ..., argn)o pid = wait()o exit(status)The Shell:o cmd arg1 ... argno stdio & I/O redirectiono filters & pipeso multi-tasking from a single shello shell is just a programTraps:o hardware interruptso software signalso trap to system