Introduction CS 111 Winter 2020 Operating System Principles Harry

Introduction CS 111 Winter 2020 Operating System Principles Harry Xu CS 111 Winter 2020 Lecture 1 Page 1

Outline Administrative materials Introduction to the course – Why study operating systems? – Basics of operating systems CS 111 Winter 2020 Lecture 1 Page 2

Administrative Issues Instructor and TAs Load and prerequisites Web site, syllabus, reading, and lectures Exams, homework, projects Grading Academic honesty CS 111 Winter 2020 Lecture 1 Page 3

Instructor: Harry Xu Associate Professor at UCLA Computer Science Department Long history of research in software systems Email: [email protected] Office: 496A Engineering VI – Office hours: W 12-1:30pm – Location: 466 Engineering VI CS 111 Winter 2020 Lecture 1 Page 4

TAs 1E: Alexandre Tiard 1F: Rishab Doshi 1B: Karen Quadros 1G: Nikita Sivakumar 1C: Howard Xie Sections can be found on CCLE CS 111 Winter 2020 Lecture 1 Page 5

Instructor/TA Division of Responsibilities Instructor handles all lectures, readings, and tests – Ask me about issues related to these TAs handle projects – Ask them about issues related to these Generally, instructor won’t be involved with project issues – So direct those questions to the TAs CS 111 Winter 2020 Lecture 1 Page 6

Web Site http://web.cs.ucla.edu/ harryxu/courses/111/ winter20 https://piazza.com/class/k4x6oonkcge2mj What’s there: – Schedules for reading, lectures, exams, projects – Project materials And uploads of completed projects – Copies of lecture slides (Powerpoint and PDF) – Announcements – Sample midterm and final problems CS 111 Winter 2020 Lecture 1 Page 7

Prerequisite Subject Knowledge CS 32 programming – Objects, data structures, queues, stacks, tables, trees CS 33 systems programming – Assembly language, registers, memory – Linkage conventions, stack frames, register saving CS 35L Software Construction Laboratory – Useful software tools for systems programming If you haven’t taken these classes, expect to have a hard time in 111 CS 111 Winter 2020 Lecture 1 Page 8

Course Format Two weekly reading assignments – Mostly from the primary text – Some supplementary materials available on web Two weekly lectures Four (10-25 hour) individual projects – Exploring and exploiting OS features – Plus one warm-up project A midterm and a final exam CS 111 Winter 2020 Lecture 1 Page 9

Course Load Reputation: THE hardest undergrad CS class – Fast pace through much non-trivial material Expectations you should have – lectures – reading – projects – exam study 4-6 hours/week 3-6 hours/week 3-20 hours/week 5-15 hours (twice) Keeping up (week by week) is critical – Catching up is extremely difficult CS 111 Winter 2020 Lecture 1 Page 10

Primary Text for Course Remzi and Andrea Arpaci-Dusseau: Operating Systems: Three Easy Pieces – Freely available on line at http://pages.cs.wisc.edu/ remzi/OSTEP/ Supplemented with web-based materials CS 111 Winter 2020 Lecture 1 Page 11

Course Grading Basis for grading: – – – – 1 midterm exam 25% Final exam 30% Lab 0 5% Other labs 10% each I do look at distribution for final grades – But don’t use a formal curve All scores available on MyUCLA – Please check them for accuracy CS 111 Winter 2020 Lecture 1 Page 12

Midterm Examination When: 5th week (in class section, Wednesday, May 1) Scope: All material up to the exam date – Approximately 60% lecture, 40% text – No questions on purely project materials Format: – Closed book – 10-15 essay questions with short answers Goals: – Test understanding of key concepts – Test ability to apply principles to practical problems CS 111 Winter 2020 Lecture 1 Page 13

Final Exam When: Monday, June 12, 3-6 PM Scope: Entire course Format: – Similar to the midterm – Covering entire scope of class – Again, no questions purely from projects Goals: – Determining if you have mastered the full range of material presented in the class CS 111 Winter 2020 Lecture 1 Page 14

Format: Lab Projects – 1 warm-up project – 4 regular projects – Done individually (except project 3) Goals: – Develop ability to exploit OS features – Develop programming/problem solving ability – Practice software project skills CS 111 Winter 2020 Lecture 1 Page 15

Late Assignments & Make-ups Lab policy – – – – Due dates are set by TAs No slip days allowed X days late 2X-1 points deducted The TAs will handle all issues related to labs Ask them, not me Don’t expect me to overrule their decisions Exams – Alternate times or make-ups only possible with prior consent of the instructor – If you miss a test, too bad CS 111 Winter 2020 Lecture 1 Page 16

Academic Honesty It is OK to study with friends – Discussing problems helps you to understand them It is OK to do independent research on a subject – There are many excellent treatments out there But all work you submit must be your own – – – – Do not write your lab answers with a friend Do not copy another student's work Do not turn in solutions from off the web If you do research on a problem, cite your sources I decide when two assignments are too similar – And I forward them immediately to the Dean If you need help, ask the instructor CS 111 Winter 2020 Lecture 1 Page 17

Academic Honesty – Projects Do your own projects – If you need additional help, ask the TA You must design and write all your own code – – – – Do not ask others how they solved the problem Do not copy solutions from the web, files or listings Cite any research sources you use Exception: project 3 allows two-person teams Protect yourself – Do not show other people your solutions – Be careful with old listings CS 111 Winter 2020 Lecture 1 Page 18

Academic Honesty and the Internet You might be able to find existing answers to some of the assignments on line Remember, if you can find it, so can we We will a plagiarism detection software It IS NOT OK to copy the answers from other people’s old assignments – People who tried that have been caught and referred to the Office of the Dean of Students ANYTHING you get off the Internet must be treated as reference material – If you use it, quote it and reference it CS 111 Winter 2020 Lecture 1 Page 19

Introduction to the Course Purpose of course and relationships to other courses Why study operating systems? What is an operating system? CS 111 Winter 2020 Lecture 1 Page 20

What Will CS 111 Do? Build on concepts from other courses – Data structures, programming languages, assembly language programming, computer architectures, . Prepare you for advanced courses – Data bases, data mining, and distributed computing – Security, fault-tolerance, high availability – Network protocols, computer system modelling Provide you with foundation concepts – Processes, threads, virtual address space, files – Capabilities, synchronization, leases, deadlock CS 111 Winter 2020 Lecture 1 Page 21

Why Study Operating Systems? Why do we have them, in the first place? Why are they important? What do they do for us? CS 111 Winter 2020 Lecture 1 Page 22

Starting From the Bottom Here’s what you’ve got CS 111 Winter 2020 Here’s what you want Lecture 1 Page 23

What Can You Do With What You’ve Got? Read or write some binary words MOV ADD JMP SQRTPD READ REQUEST SENSE Report X and Y movements Write to groups of pixels Read or write a block of data CS 111 Winter 2020 Lecture 1 Page 24

You’re Going to Need Some Help And that’s what the operating system is about Helping you perform complex operations – Using various hardware – And probably various bits of software While hiding the complexity And making sure nothing gets in the way of anything else CS 111 Winter 2020 Lecture 1 Page 25

What Is An Operating System, Anyway? System software intended to provide support for higher level applications – Some higher level system software applications – But primarily for user processes The software that sits between the hardware and everything else The software that hides nasty details – Of hardware, software, and common tasks On a good day, the OS is your best computing friend CS 111 Winter 2020 Lecture 1 Page 26

But Why Are You Studying Them? High probability none of you will ever write an operating system – Or even fix an operating system bug Not very many different operating systems are in use – So the number of developers for them is small So why should you care about them? CS 111 Winter 2020 Lecture 1 Page 27

Everybody Has One Practically all computing devices you will ever use has an operating system – Servers, laptops, desktop machines, tablets, smart phones, game consoles, set-top boxes Many things you don’t think of as computers have CPUs inside – Usually with an operating system – Internet of Things devices So you will work with operating systems CS 111 Winter 2020 Lecture 1 Page 28

How Do You Work With OSes? You configure them You use their features when you write programs You rely on services that they offer – Memory management – Persistent storage – Scheduling and synchronization – Interprocess communications – Security CS 111 Winter 2020 Lecture 1 Page 29

Another Good Reason Many hard problems have been tackled in the context of operating systems – How to coordinate separate computations – How to manage shared resources – How to virtualize hardware and software – How to organize communications – How to protect your computing resources The operating system solutions are often applicable to programs and systems you write CS 111 Winter 2020 Lecture 1 Page 30

What Is An Operating System? Many possible definitions One is: – It is low level software . . . – That provides better, more usable abstractions of the hardware below it – To allow easy, safe, fair use and sharing of those resources CS 111 Winter 2020 Lecture 1 Page 31

What Does an OS Do? It manages hardware for programs – Allocates hardware and manages its use – Enforces controlled sharing (and privacy) – Oversees execution and handles problems It abstracts the hardware – Makes it easier to use and improves SW portability – Optimizes performance It provides new abstractions for applications – Powerful features beyond the bare hardware CS 111 Winter 2020 Lecture 1 Page 32

What Does An OS Look Like? A set of management & abstraction services – Invisible, they happen behind the scenes Applications see objects and their services – CPU supports data-types and operations bytes, shorts, longs, floats, pointers, . add, subtract, copy, compare, indirection, . – So does an operating system, but at a higher level files, processes, threads, devices, ports, . create, destroy, read, write, signal, . An OS extends a computer – Creating a much richer virtual computing platform CS 111 Winter 2020 Supporting richer objects, more powerful operations Lecture 1 Page 33

Where Does the OS Fit In? Applications Software (e.g. word processor, compiler, VOIP program, .) Application Binary Interface System Services/Libraries (e.g. string, random #s, encryption, graphics .) System Call Interface Operating System Privileged instruction set Standard instruction set Hardware(arithmetic, logical, copy, test, flow-control operations, .) CS 111 Winter 2020 Lecture 1 Page 34

Instruction Set Architectures (ISAs) The set of instructions supported by a computer – Which bit patterns correspond to what operations There are many different ISAs (all incompatible) – – – – Different word/bus widths (8, 16, 32, 64 bit) Different features (low power, DSPs, floating point) Different design philosophies (RISC vs. CISC) Competitive reasons (68000, x86, PowerPC) They usually come in families – Newer models add features (e.g., Pentium vs. 386) – But remain upwards-compatible with older models A program written for an ISA will run on any compliant CPU CS 111 Winter 2020 Lecture 1 Page 35

Privileged vs. General Instructions Most modern ISAs divide the instruction set into privileged vs. general Any code running on the machine can execute general instructions Processor must be put into a special mode to execute privileged instructions – Usually only in that mode when the OS is running – Privileged instructions do things that are “dangerous” CS 111 Winter 2020 Lecture 1 Page 36

Portability to Multiple ISAs A successful OS will run on many ISAs – Some customers cannot choose their ISA – If you don’t support it, you can’t sell to them Which implies that the OS will abstract the ISA Minimal assumptions about specific HW – General frameworks are HW independent File systems, protocols, processes, etc. – HW assumptions isolated to specific modules Context switching, I/O, memory management – Careful use of types Word length, sign extension, byte order, alignment How can an OS manufacturer distribute to all these different ISAs and platforms? CS 111 Winter 2020 Lecture 1 Page 37

Distribution Binary is the derivative of source – The OS is written in source – But a source distribution must be compiled – A binary distribution is ready to run OSes usually distributed in binary One binary distribution per ISA Binary model for platform support – Device drivers can be added, after-market Can be written and distributed by 3rd parties Same driver works with many versions of OS CS 111 Winter 2020 Lecture 1 Page 38

Interface Stability People want new releases of an OS – New features, bug fixes, enhancements People also fear new releases of an OS – OS changes can break old applications How can we prevent such problems? – Define well specified Application Interfaces 1. Application programming interfaces (APIs) 2. Application binary interfaces (ABIs) – Applications only use committed interfaces – OS vendors preserve upwards-compatibility CS 111 Winter 2020 Lecture 1 Page 39

The OS and Abstraction One major function of an OS is to offer abstract versions of resources – As opposed to actual physical resources Essentially, the OS implements the abstract resources using the physical resources – E.g., processes (an abstraction) are implemented using the CPU and RAM (physical resources) – And files (an abstraction) are implemented using disks (a physical resource) CS 111 Winter 2020 Lecture 1 Page 40

Why Abstract Resources? The abstractions are typically simpler and better suited for programmers and users – Easier to use than the original resources E.g., don’t need to worry about keeping track of disk interrupts – Compartmentalize/encapsulate complexity E.g., need not be concerned about what other executing code is doing and how to stay out of its way – Eliminate behavior that is irrelevant to user E.g., hide the slow erase cycle of flash memory – Create more convenient behavior E.g., make it look like you have the network interface entirely for your own use CS 111 Winter 2020 Lecture 1 Page 41

Common Types of OS Resources Serially reusable resources Partitionable resources Sharable resources CS 111 Winter 2020 Lecture 1 Page 42

Serially Reusable Resources Used by multiple clients, but only one at a time – Time multiplexing Require access control to ensure exclusive use Require graceful transitions from one user to the next Examples: CS 111 Winter 2020 Lecture 1 Page 43

What Is A Graceful Transition? A switch that totally hides the fact that the resource used to belong to someone else – Don’t allow the second user to access the resource until the first user is finished with it No incomplete operations that finish after the transition – Ensure that each subsequent user finds the resource in “like new” condition CS 111 Winter 2020 No traces of data or state left over from the first user Lecture 1 Page 44

Partitionable Resources Divided into disjoint pieces for multiple clients – Spatial multiplexing Needs access control to ensure: – Containment: you cannot access resources outside of your partition – Privacy: nobody else can access resources in your partition Examples: CS 111 Winter 2020 Lecture 1 Page 45

Do We Still Need Graceful Transitions? Yes Most partitionable resources aren’t permanently allocated – The piece of RAM you’re using now will belong to another process later As long as it’s “yours,” no transition required But sooner or later it’s likely to become someone else’s CS 111 Winter 2020 Lecture 1 Page 46

Shareable Resources Usable by multiple concurrent clients – Clients don’t “wait” for access to resource – Clients don’t “own” a particular subset of the resource May involve (effectively) limitless resources – Air in a room, shared by occupants – Copy of the operating system, shared by processes CS 111 Winter 2020 Lecture 1 Page 47

Do We Still Need Graceful Transitions? Typically not The shareable resource usually doesn’t change state Or isn’t “reused” We never have to clean up what doesn’t get dirty – Like an execute-only copy of the OS Shareable resources are great! – When you can have them . . . Tip: Design your system to maximize sharable resources. CS 111 Winter 2020 Lecture 1 Page 48

General OS Trends They have grown larger and more sophisticated Their role has fundamentally changed – – – – From shepherding the use of the hardware To shielding the applications from the hardware To providing powerful application computing platform To becoming a sophisticated “traffic cop” They still sit between applications and hardware Best understood through services they provide – Capabilities they add – Applications they enable – Problems they eliminate CS 111 Winter 2020 Lecture 1 Page 49

Why? Ultimately because it’s what users want The OS must provide core services to applications Applications have become more complex – More complex internal behavior – More complex interfaces – More interactions with other software The OS needs to help with all that complexity CS 111 Winter 2020 Lecture 1 Page 50

OS Convergence There are a handful of widely used OSes 1991 1985 1984 And a few special purpose ones (e.g., real time and embedded system OSes) OSes in the same family are used for vastly different purposes Challenging for the OS designer Most OSes are based on pretty old models CS 111 Winter 2020 Lecture 1 Page 51

Why Have OSes Converged? They’re expensive to build and maintain – So it’s a hard business to get into and stay in They only succeed if users choose them over other OS options – Which can’t happen unless you support all the apps the users want – Which requires other parties to do a lot of work You need to have some clear advantage over present acceptable alternatives CS 111 Winter 2020 Lecture 1 Page 52

Conclusion Understanding operating systems is critical to understanding how computers work Operating systems interact directly with the hardware Operating systems provide services via abstractions Operating systems are constrained by many non-technical factors CS 111 Winter 2020 Lecture 1 Page 53