CS 423 Operating System Design: Overview And Basic Concepts

CS 423Operating System Design:Overview and BasicConceptsProfessor Adam BatesFall 2018CS423: Operating Systems Design

Goals for Today Learning Objectives: Introduce OS definition, challenges, and historyAnnouncements: C4 readings for Week 2 are out! Due Jan 26 MP0 is available on Compass! Due Jan 29 HW0 is available on Compass! Due Jan 29Reminder: Please put awaydevices at the start of classCS 423: Operating Systems Design2

What is an operating system?CS 423: Operating Systems Design3

Why Operating Systems?Software to manage a computer’s resources for itsusers and applications.Application SoftwareWeb ServerBrowserSlackPop MailOperating SystemRead/WriteStandardOutputHardwareCS 423: Operating Systems DesignDeviceControlFileSystemCommunicationNetwork4

Why Operating Systems?Software to manage a computer’s resources for itsusers and applications.Application SoftwareWeb ServerBrowserSlackPop MailSystem LibrarySystem LibrarySystem LibrarySystem LibraryOperating SystemRead/WriteStandardOutputHardwareCS 423: Operating Systems DesignDeviceControlFileSystemCommunicationNetwork5

Why Operating Systems?The OS exports a user interface. Why?Application SoftwareWeb ServerBrowserSlackPop MailSystem LibrarySystem LibrarySystem LibrarySystem LibraryStandard Operating System InterfaceOperating SystemRead/WriteStandardOutputHardwareCS 423: Operating Systems DesignDeviceControlFileSystemCommunicationNetwork6

Why Operating Systems?Standard interface increases portability and reducesthe need for machine-specific code.Application SoftwareWeb ServerBrowserSlackPop MailSystem LibrarySystem LibrarySystem LibrarySystem LibraryStandard Operating System InterfaceOperating System (machine independent emCommunicationMachine specific partHardwareCS 423: Operating Systems DesignNetwork7

Why Operating Systems?OS Runs on Multiple Platforms while presenting the sameInterface:Application SoftwareBrowserSlackPop MailStandard Operating System InterfaceOperating System (machine independent emCommunicationHardwareAbstractionLayerWeb ServerMachine specific partHardwareCS 423: Operating Systems DesignNetwork8

What are the responsibilitiesof an operating system?CS 423: Operating Systems Design9

Operating System RolesRole #1: Referee Manage resource alloca3on between usersand applica3ons Isolate different users and applica3ons fromone another Facilitate and mediate communica3onbetween different users and applica3onsCS423: Operating Systems Design10

Operating System RolesRole #2: Illusionist Allow each applica3on to believe it has theen3re machine to itself Create the appearance of an Infinite numberof processors, (near) infinite memory Abstract away complexity of reliability,storage, network communica3on CS423: Operating Systems Design11

Operating System RolesRole #3: Glue Manage hardware so applica3ons can bemachine-agnos3c Provide a set of common services thatfacilitate sharing among applica3ons Examples of “Glue” OS Services?CS423: Operating Systems Design12

Operating System RolesRole #3: Glue Manage hardware so applica3ons can bemachine-agnos3c Provide a set of common services thatfacilitate sharing among applica3ons Examples of “Glue” OS Services? Cut-and-paste, File I/O, User Interfaces.CS423: Operating Systems Design13

Consider file systems and storage devices How is the OS a referee?An illusionist?Glue?CS 423: Operating Systems Design14

Ex: File System SupportReferee Prevent users from accessing each other’s files withoutpermission Even aUer a file is dele3ng and its space re-usedIllusionist Files can grow (nearly) arbitrarily large Files persist even when the machine crashes in the middleof a saveGlue Named directories, prinW, other system calls for File I/OCS 423: Operating Systems Design15

A QuestionWhat does an OSneed to do inorder safely runan untrustworthyapplication?CS423: Operating Systems Design16

Another QuestionHow should anoperating systemallocate processingtime betweencompeting uses?CS423: Operating Systems Design17

Example: Web Service(1)(2)HTTP GET index.htmlRead file: index.htmlClient Serverindex.html(4)(3)HTTP web pageFile dataHow does the server manage many simultaneous clientrequests?How do we keep the client safe from spyware embeddedin scripts on a web site?How do handles updates to the web site such that clientsalways see a consistent view?CS 423: Operating Systems Design18

OS ChallengesReliability Does the system do what it was designed to do?Availability What por3on of the 3me is the system working? Mean Time To Failure (MTTF), Mean Time to RepairSecurity Can the system be compromised by an a acker?Privacy Data is accessible only to authorized usersCS423: Operating Systems Design19

OS ChallengesPortability For programs:Applica3on programming interface (API)Abstract virtual machine (AVM) For hardwareHardware abstrac3on rarySystemLibraryKernel-user Interface(Abstract virtual machine)Kernel-modeFile SystemVirtual MemoryTCP/IP NetworkingSchedulingHardware Abstraction LayerHardware-Specific Softwareand Device DriversProcessorsHardwareAddress TranslationDiskGraphics ProcessorCS423: Operating Systems DesignNetwork20

OS ChallengesPerformanceLatency/response 3meHow long does an opera3on take to complete?ThroughputHow many opera3ons can be done per unit of 3me?OverheadHow much extra work is done by the OS?FairnessHow equal is the performance received by different users?PredictabilityHow consistent is the performance over 3me?CS423: Operating Systems Design21

OS Family TreeMVSMS/DOSVMSMulticsLevel 1UNIXLevel 2VM/370WindowsBSD UNIXWindows NTVMWareMachLinuxWindows 8NEXTLevel 3MacOSLevel 4MacOS XLevel 5iOSLevel 6InfluenceDescendantCS423: Operating Systems DesignAndroid22

Performance / Time1.3 Operating Systems: Past, Present, and FutureFactor(2014/1981)198119972014Uniprocessor speed (MIPS)120025002.5KCPUs per computer1110 10 Processor MIPS/ 100K 25 0.20500KDRAM Capacity (MiB)/ 0.00221K500KDisk Capacity (GiB)/ 0.003725K10M300 bps256 Kbps20 Mbps100K10 Mbps(shared)100 Mbps 10 Gbps(switched) (switched)Home InternetMachine room networkRatio of usersto computers100:11:11:several1000100 Approximate computer server performance over time, reflecting the most widely used seOperatingSystems Design23nCS423:1981,a minicomputer;in 1997, a high-end workstation; in 2014, a rack-mounted multic

Early Operating SystemsOne applica3on at a 3me Had complete control of hardware OS was run3me library Users would stand in line to use the computerBatch systems Keep CPU busy by having a queue of jobs OS would load next job while current one runs Users would submit jobs, and wait, and wait, andCS423: Operating Systems Design24

Time-Sharing OSsMul3ple users on computer at same 3me Mul3programming: run mul3ple programs atsame 3me Interac3ve performance: try to completeeveryone’s tasks quickly As computers became cheaper, more importantto op3mize for user 3me, not computer 3meCS423: Operating Systems Design25

Today’s OSs Smartphones Embedded Laptopssystems Tablets Virtualmachines Data center serversCS423: Operating Systems Design26

Tomorrow’s OSsGiant-scale data centers Increasing numbers of processors percomputer Increasing numbers of computers per user Very large scale storage CS423: Operating Systems Design27

that these fundamental operating system challenges will persist. Early Operating Systems Computers were expensive; users would wait. The first operating systems were runtime libraries intended to simplify the programming of early computer systems. Rather than the tiny, inexpensive yet massively complex hardware and software systems of today .