EECS 3221:
OPERATING SYSTEM FUNDAMENTALS
Hamzeh Khazaei
Department of Electrical Engineering and Computer Science
Week 1, Module 2: Introduction to Operating Systems
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Chapter 1: Introduction
! What Operating Systems Do
! Computer-System Organization
! Computer-System Architecture
! Operating-System Operations
! Resource Management
! Security and Protection
! Virtualization
! Distributed Systems
! KernelDataStructures
! Computing Environments or Pardigms
! Free/Libre and Open-Source Operating Systems
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Computer System Structure
! Computer system can be divided into four components: ! Hardware – provides basic computing resources
4CPU, memory, I/O devices ! Operating system
4Controls and coordinates use of hardware among various applications and users
! Application programs – define the ways in which the system resources are used to solve the computing problems of the users
4Word processors, compilers, web browsers, database systems, video games
! Users
4People, machines, other computers
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Abstract View of Components of Computer
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What Operating Systems Do
! Dependsonthepointofview
! Userswantconvenience,easeofuseandgoodperformance
! Don’tcareaboutresourceutilization
! Butsharedcomputersuchasmainframeorminicomputermustkeepallusers
happy
! Operatingsystemisaresourceallocatorandcontrolprogrammaking efficient use of HW and managing execution of user programs
! Usersofdedicatesystemssuchasworkstationshavededicatedresources but frequently use shared resources from servers
! Mobile devices like smartphones and tables are resource poor, optimized for usability and battery life
! Mobileuserinterfacessuchastouchscreens,voicerecognition
! Somecomputershavelittleornouserinterface,suchasembeddedcomputers
in devices and automobiles
! Runprimarilywithoutuserintervention
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Defining Operating Systems
! Term OS covers many roles
! Because of myriad designs and uses of OSes
! Present in toasters through ships, spacecraft, game machines, TVs and industrial control systems
! Born when fixed use computers for military became more general purpose and needed resource management and program control
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Operating System Definition (Cont.)
! No universally accepted definition
! “Everything a vendor ships when you order an operating system” is a good
approximation
! But varies wildly
! “The one program running at all times on the computer” is the kernel, part of the operating system
! Everything else is either
! a system program (ships with the operating system, but not part of the
kernel), or
! an application program, all programs not associated with the operating system
! Today’sOSesforgeneralpurposeandmobilecomputingalsoinclude middleware – a set of software frameworks that provide addition services to application developers such as databases, multimedia, graphics
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Computer System Organization
! Computer-system organization
! One or more CPUs, device controllers connect through common bus
providing access to shared memory
! Concurrent execution of CPUs and devices competing for memory cycles
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Computer-System Operation
! I/O devices and the CPU can execute concurrently
! Each device controller is in charge of a particular device type
! Each device controller has a local buffer
! Each device controller type has an operating system device driver to manage it
! CPU moves data from/to main memory to/from local buffers
! I/O is from the device to local buffer of controller
! Device controller informs CPU that it has finished its operation by causing an interrupt
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Common Functions of Interrupts
! Interrupttransferscontroltotheinterruptserviceroutinegenerally,through the interrupt vector, which contains the addresses of all the service routines
! Interrupt architecture must save the address of the interrupted instruction
! Atraporexceptionisasoftware-generatedinterruptcausedeitherbyan
error or a user request
! Anoperatingsystemisinterruptdriven
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Interrupt Timeline
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! bootstrap program is loaded at power-up or reboot
! Typically stored in ROM or EPROM, generally known as firmware
! Initializes all aspects of system
! Loads operating system kernel and starts execution
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Computer Startup
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Interrupt Handling
! TheoperatingsystempreservesthestateoftheCPUbystoringregisters and the program counter
! Determineswhichtypeofinterrupthasoccurred: ! polling
! vectored interrupt system
! Separate segments of code determine what action should be taken for each
type of interrupt
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Interrupt-drive I/O Cycle
CPU 1
CPU executing checks for interrupts between instructions
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I/O controller
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device driver initiates I/O
initiates I/O
CPU receiving interrupt, transfers control to interrupt handler
input ready, output
complete, or error generates interrupt signal
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interrupt handler
processes data, returns from interrupt
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CPU resumes processing of interrupted task
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I/O Structure
! AfterI/Ostarts,controlreturnstouserprogramonlyuponI/Ocompletion
! Wait instruction idles the CPU until the next interrupt
! Wait loop (contention for memory access)
! At most one I/O request is outstanding at a time, no simultaneous I/O processing
! AfterI/Ostarts,controlreturnstouserprogramwithoutwaitingforI/O completion
! System call – request to the OS to allow user to wait for I/O completion
! Device-status table contains entry for each I/O device indicating its
type, address, and state
! OS indexes into I/O device table to determine device status and to modify table entry to include interrupt
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Storage Structure
! Main memory – only large storage media that the CPU can access directly
! Random access
! Typically volatile
! Typically random-access memory in the form of Dynamic Random-access Memory (DRAM)
! Secondary storage – extension of main memory that provides large nonvolatile storage capacity
! Hard Disk Drives (HDD) – rigid metal or glass platters covered with magnetic recording material
! Disk surface is logically divided into tracks, which are subdivided into sectors
! The disk controller determines the logical interaction between the device and the computer
! Non-volatile memory (NVM) devices– faster than hard disks, nonvolatile
! Various technologies
! Becoming more popular as capacity and performance increases, price drops
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Storage Definitions and Notation Review
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The basic unit of computer storage is the bit . A bit can contain one of two values, 0 and 1. All other storage in a computer is based on collections of bits. Given enough bits, it is amazing how many things a computer can represent: numbers, letters, images, movies, sounds, documents, and programs, to name a few. A byte is 8 bits, and on most computers it is the smallest convenient chunk of storage. For example, most computers don’t have an instruction to move a bit but do have one to move a byte. A less common term is word, which is a given computer architecture’s native unit of data. A word is made
up of one or more bytes. For example, a computer that has 64-bit registers and 64-bit memory addressing typically has 64-bit (8-byte) words. A computer executes many operations in its native word size rather than a byte at a time.
Computer storage, along with most computer throughput, is generally
measured and manipulated in bytes and collections of bytes. A kilobyte , or
KB , is 1,024 bytes; a megabyte , or MB , is 1,0242 bytes; a gigabyte , or GB , is 1,0243 bytes; a terabyte , or TB , is 1,0244 bytes; and a petabyte , or PB , is 1,0245 bytes. Computer manufacturers often round off these numbers and say that
a megabyte is 1 million bytes and a gigabyte is 1 billion bytes. Networking measurements are an exception to this general rule; they are given in bits (because networks move data a bit at a time).
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Storage Hierarchy
! Storage systems organized in hierarchy ! Speed
! Cost
! Volatility
! Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage
! Device Driver for each device controller to manage I/O
! Provides uniform interface between controller and kernel
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Storage-Device Hierarchy
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How a Modern Computer Works
A von Neumann architecture
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Direct Memory Access Structure
! Used for high-speed I/O devices able to transmit information at close to memory speeds
! Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention
! Only one interrupt is generated per block, rather than the one interrupt per byte
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Computer-System Architecture
! Most systems use a single general-purpose processor
! Most systems have special-purpose processors as well
! Multiprocessors systems growing in use and importance
! Also known as parallel systems, tightly-coupled systems ! Advantages include:
1. Increased throughput
2. Economy of scale
3. Increased reliability – graceful degradation or fault tolerance
! Two types:
1. Asymmetric Multiprocessing – each processor is assigned a
specie task.
2. Symmetric Multiprocessing – each processor performs all tasks
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Symmetric Multiprocessing Architecture
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A Dual-Core Design
” Multi-chip and multicore
” Systems containing all chips
! Chassis containing multiple separate systems
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Clustered Systems
! Like multiprocessor systems, but multiple systems working together
! Usually sharing storage via a storage-area network (SAN)
! Provides a high-availability service which survives failures
4Asymmetric clustering has one machine in hot-standby mode 4Symmetric clustering has multiple nodes running applications,
monitoring each other
! Some clusters are for high-performance computing (HPC)
4 Applications must be written to use parallelization
! Some have distributed lock manager (DLM) to avoid conflicting
operations
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Clustered Systems
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PC Motherboard
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Operating-System Operations
! Bootstrap program – simple code to initialize the system, load the kernel ! Kernelloads
! Starts system daemons (services provided outside of the kernel)
! Kernel interrupt driven (hardware and software)
! Hardware interrupt by one of the devices ! Software interrupt (exception or trap):
4Software error (e.g., division by zero)
4Request for operating system service – system call
4Other process problems include infinite loop, processes modifying each other or the operating system
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Multiprogramming and Multitasking
! Multiprogramming(Batchsystem)neededforefficiency
! Single user cannot keep CPU and I/O devices busy at all times
! Multiprogramming organizes jobs (code and data) so CPU always has one to execute
! A subset of total jobs in system is kept in memory
! One job selected and run via job scheduling
! When it has to wait (for I/O for example), OS switches to another job
! Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing
! Response time should be < 1 second! Each user has at least one program executing in memory[process! If several jobs ready to run at the same time [ CPU scheduling! If processes don’t fit in memory, swapping moves them in and out to run! Virtual memory allows execution of processes not completely in memoryOperating System Concepts – 10th Edition 1.30 Silberschatz et al. © 2018 updated by Khazaei @ 202130 Dual-mode and Multimode Operation! Dual-mode operation allows OS to protect itself and other system components! User mode and kernel mode ! Mode bit provided by hardware4Provides ability to distinguish when system is running user code or kernel code4Some instructions designated as privileged, only executable in kernel mode4System call changes mode to kernel, return from call resets it to user ! Increasingly CPUs support multi-mode operations! i.e. virtual machine manager (VMM) mode for guest VMsOperating System Concepts – 10th Edition 1.32 Silberschatz et al. © 2018 updated by Khazaei @ 20213215Transition from User to Kernel Mode! Timertopreventinfiniteloop/processhoggingresources! Timer is set to interrupt the computer after some time period! Keep a counter that is decremented by the physical clock! Operating system set the counter (privileged instruction)! When counter zero generate an interrupt! Set up before scheduling process to regain control or terminate program that exceeds allotted timeOperating System Concepts – 10th Edition 1.33 Silberschatz et al. © 2018 updated by Khazaei @ 2021 33 Process Management! Aprocessisaprograminexecution.Itisaunitofworkwithinthesystem. Program is a passive entity; process is an active entity.! Processneedsresourcestoaccomplishitstask ! CPU,memory,I/O,files! Initializationdata! Processterminationrequiresreclaimofanyreusableresources! Single-threadedprocesshasoneprogramcounterspecifyinglocationofnextinstruction to execute! Processexecutesinstructionssequentially,oneatatime,untilcompletion! Multi-threadedprocesshasoneprogramcounterperthread! Typicallysystemhasmanyprocesses,someuser,someoperatingsystemrunning concurrently on one or more CPUs! ConcurrencybymultiplexingtheCPUsamongtheprocesses/threadsOperating System Concepts – 10th Edition 1.34 Silberschatz et al. © 2018 updated by Khazaei @ 20213416Process Management Activities! Theoperatingsystemisresponsibleforthefollowingactivitiesinconnection with process management:! Creating and deleting both user and system processes ! Suspending and resuming processes! Providing mechanisms for process synchronization! Providing mechanisms for process communication! Providing mechanisms for deadlock handlingOperating System Concepts – 10th Edition 1.35 Silberschatz et al. © 2018 updated by Khazaei @ 202135 Memory Management! Toexecuteaprogramall(orpart)oftheinstructionsmustbeinmemory ! All(orpart)ofthedatathatisneededbytheprogrammustbeinmemory ! Memory management determines what is in memory and when! Optimizing CPU utilization and computer response to users ! Memorymanagementactivities! Keeping track of which parts of memory are currently being used and by whom! Deciding which processes (or parts thereof) and data to move into and out of memory! Allocating and deallocating memory space as neededOperating System Concepts – 10th Edition 1.36 Silberschatz et al. © 2018 updated by Khazaei @ 20213617File-system Management! OS provides uniform, logical view of information storage! Abstracts physical properties to logical storage unit – file! Each medium is controlled by device (i.e., disk drive, tape drive)4Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random)! File-System management! Files usually organized into directories! Access control on most systems to determine who can access what ! OS activities include4Creating and deleting files and directories 4Primitives to manipulate files and directories 4Mapping files onto secondary storage4Backup files onto stable (non-volatile) storage mediaOperating System Concepts – 10th Edition 1.37 Silberschatz et al. © 2018 updated by Khazaei @ 202137 Mass-Storage Management! Usuallydisksusedtostoredatathatdoesnotfitinmainmemoryordatathat must be kept for a “long” period of time! Propermanagementisofcentralimportance! Entirespeedofcomputeroperationhingesondisksubsystemanditsalgorithms! OSactivities! Mountingandunmounting ! Free-spacemanagement ! Storageallocation! Diskscheduling! Partitioning! Protection! Somestorageneednotbefast! Tertiarystorageincludesopticalstorage,magnetictape ! Stillmustbemanaged–byOSorapplicationsOperating System Concepts – 10th Edition 1.38 Silberschatz et al. © 2018 updated by Khazaei @ 20213818Caching! Important principle, performed at many levels in a computer (in hardware, operating system, software)! Information in use copied from slower to faster storage temporarily! Faster storage (cache) checked first to determine if information is there! If it is, information used directly from the cache (fast)! If not, data copied to cache and used there! Cache smaller than storage being cached! Cache management important design problem ! Cache size and replacement policyOperating System Concepts – 10th Edition 1.39 Silberschatz et al. © 2018 updated by Khazaei @ 202139 Characteristics of Various Types of StorageMovement between levels of storage hierarchy can be explicit or implicitOperating System Concepts – 10th Edition 1.40 Silberschatz et al. © 2018 updated by Khazaei @ 2021 4019Migration of data “A” from Disk to Register! Multitaskingenvironmentsmustbecarefultousemostrecentvalue,no matter where it is stored in the storage hierarchy! Multiprocessorenvironmentmustprovidecachecoherencyinhardware such that all CPUs have the most recent value in their cache! Distributed environment situation even more complex! Several copies of a datum can exist (aka replication factor) ! Various solutions covered in Chapter 19Operating System Concepts – 10th Edition 1.41 Silberschatz et al. © 2018 updated by Khazaei @ 2021 41 Protection and Security! Protection – any mechanism for controlling access of processes or users to resources defined by the OS! Security – defense of the system against internal and external attacks! Huge range, including denial-of-service, worms, viruses, identity theft,theft of service! Systems generally first distinguish among users, to determine who can do what! User identities (user IDs, security IDs) include name and associated number, one per user! User ID then associated with all files, processes of that user to determine access control! Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file! Privilege escalation allows user to change to effective ID with more rightsOperating System Concepts – 10th Edition 1.43 Silberschatz et al. © 2018 updated by Khazaei @ 20214320Virtualization! AllowsoperatingsystemstorunapplicationswithinotherOSes ! Vast and growing industry! Emulation used when source CPU type different from target type (i.e. PowerPC to Intel x86)! Generally slowest method! When computer language not compiled to native code – Interpretation! Virtualization – OS natively compiled for CPU, running guest OSes also natively compiled! Consider VMware running Win10 guests, each running applications, all on native Win10 host OS! VMM (virtual machine Manager) provides virtualization servicesOperating System Concepts – 10th Edition 1.44 Silberschatz et al. © 2018 updated by Khazaei @ 202144 Virtualization (cont.)! Use cases involve laptops and desktops running multiple OSes for exploration or compatibility (type 2)! Apple laptop running Mac OS X host, Windows as a guest! Developing apps for multiple OSes without having multiple systems ! QA testing applications without having multiple systems! Executing and managing compute environments within data centers! VMM can run natively, in which case they are also the host (type 1) ! There is no general-purpose host then (VMware ESX and CitrixXenServer)Operating System Concepts – 10th Edition 1.45 Silberschatz et al. © 2018 updated by Khazaei @ 20214521Computing Environments – Virtualizationprocesses processes processes kernel kernel kernel VM1 VM2 VM3 virtual machinemanager hardware processes kernel hardware programming interface(a)(b)Operating System Concepts – 10th Edition1.46Silberschatz et al. © 2018 updated by Khazaei @ 2021 46 End.Operating System Concepts – 10h Edition4722THE REST OF SLIDES FOR YOUR READING.Operating System Concepts – 10th Edition 1.48 Silberschatz et al. © 2018 updated by Khazaei @ 2021 48 Distributed Systems! Distributed computing! Collection of separate, possibly heterogeneous, systems networkedtogether4Network is a communications path, TCP/IP most common– Local Area Network (LAN)– Wide Area Network (WAN)– Metropolitan Area Network (MAN) – Personal Area Network (PAN)! Network Operating System provides features between systems across network4Communication scheme allows systems to exchange messages 4Illusion of a single systemOperating System Concepts – 10th Edition 1.49 Silberschatz et al. © 2018 updated by Khazaei @ 20214923Kernel Data Structures! Many similar to standard programming data structures ! Singly linked list data data! Doubly linked listdata null data! Circular linked list dataOperating System Concepts – 10th Editiondatadatanulldata nulldata•••Silberschatz et al. © 2018 updated by Khazaei @ 2021 •••••• datadata 1.50 50 ” Binary search tree left <= right! Search performance is O(n)! Balanced binary search tree is O(lg n)Kernel Data Structures 121714 3235 Operating System Concepts – 10th Edition6401.51 Silberschatz et al. © 2018 updated by Khazaei @ 2021 5124Kernel Data Structures ” Hash function can create a hash map hash_function(key)01..nvaluehash map” Bitmap – string of n binary digits representing the status of n items” Linux data structures defined in include files
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Computing Environments – Traditional
! Stand-alone general-purpose machines
! But blurred as most systems interconnect with others (i.e., the Internet)
! Portals provide web access to internal systems
! Network computers (thin clients) are like Web terminals
! Mobile computers interconnect via wireless networks
! Networking becoming ubiquitous – even home systems use firewalls to protect home computers from Internet attacks
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Computing Environments – Mobile
! Handheldsmartphones,tablets,etc
! What is the functional difference between them and a “traditional” laptop? ! Extra feature – more OS features (GPS, gyroscope)
! Allowsnewtypesofappslikeaugmentedreality
! Use IEEE 802.11 wireless, or cellular data networks for connectivity
! Leaders are Apple iOS and Google Android
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Computing Environments – Client-Server
! Client-Server Computing
! Dumb terminals supplanted by smart PCs
! Many systems now servers, responding to requests generated by clients
4 Compute-server system provides an interface to client to request services (i.e., database)
4 File-server system provides interface for clients to store and retrieve files
Server
Network
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client desktop
client laptop
client smartphone
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Computing Environments – Peer-to-Peer
! Anothermodelofdistributedsystem
! P2P does not distinguish clients and servers
! Instead all nodes are considered peers ! May each act as client, server or both ! Node must join P2P network
4Registers its service with central lookup service on network, or
4Broadcast request for service and respond to requests for service via discovery protocol
! Examples include Napster and Gnutella, Voice over IP (VoIP) such as Skype and torrent
client
client
client
client
client
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Computing Environments – Cloud Computing
” Delivers computing, storage, even apps as a service across a network
” Logical extension of virtualization because it uses virtualization as the base for its functionality.
! Amazon EC2 has thousands of servers, millions of virtual machines, petabytes of storage available across the Internet, pay based on usage
” Many types
! Public cloud – available via Internet to anyone willing to pay
! Private cloud – run by a company for the company’s own use
! Hybrid cloud – includes both public and private cloud components
! Software as a Service (SaaS) – one or more applications available via the Internet (i.e., word processor)
! Platform as a Service (PaaS) – software stack ready for application use via the Internet (i.e., a database server)
! Infrastructure as a Service (IaaS) – servers or storage available over Internet (i.e., storage available for backup use)
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Cloud Computing
https://www.youtube.com/watch?v=dH0yz-Osy54
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Computing Environments – Cloud Computing
! CloudcomputingenvironmentscomposedoftraditionalOSes,plusVMMs, plus cloud management tools
! Internet connectivity requires security like firewalls
! Load balancers spread traffic across multiple applications
Internet
firewall
load balancer
customer requests
servers
servers
cloud management commands
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cloud customer interface
virtual machines
virtual machines
storage
cloud managment services
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Computing Environments – Real-Time Embedded Systems
! Real-time embedded systems most prevalent form of computers
! Vary considerable, special purpose, limited purpose OS, real-time OS ! Use expanding
! Many other special computing environments as well
! Some have OSes, some perform tasks without an OS
! Real-time OS has well-defined fixed time constraints ! Processing must be done within constraint
! Correct operation only if constraints met
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Free and Open-Source Operating Systems
! Operating systems made available in source-code format rather than just binary closed-source and proprietary
! Counter to the copy protection and Digital Rights Management (DRM) movement
! StartedbyFreeSoftwareFoundation(FSF),whichhas“copyleft”GNU Public License (GPL)
! Free software and open-source software are two different ideas championed by different groups of people
4 http://gnu.org/philosophy/open-source-misses-the-point.html/
! Examples include GNU/Linux and BSD UNIX (including core of Mac OS
X), and many more
! Can use VMM like VMware Player (Free on Windows), Virtualbox (open
source and free on many platforms – http://www.virtualbox.com) ! Use to run guest operating systems for exploration
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The Study of Operating Systems
There has never been a more interesting time to study operating systems, and it has never been easier. The open-source movement has overtaken operating systems, causing many of them to be made available in both source and binary (executable) format. The list of operating
systems available in both formats includes Linux, BUSD UNIX, Solaris, and part of macOS.
The availability of source code allows us to study operating systems from the inside out. Questions that we could once answer only by looking at documentation or the behavior of an operating system we can now answer by examining the code itself.
Operating systems that are no longer commercially viable have been open-sourced as well, enabling us to study how systems operated in a time of fewer CPU, memory, and storage resources.
An extensive but incomplete list of open-source operating-system projects is available
from https://curlie.org/Computers/Software/Operating_Systems/Open_Source/
In addition, the rise of virtualization as a mainstream (and frequently free) computer function makes it possible to run many operating systems on top of one core system. For example, VMware (http://www.vmware.com) providesa free “player” for Windows on which hundreds of free
“virtual appliances” can run. Virtualbox (http://www.virtualbox.com) provides a free, open-source virtual machine manager on many operating systems. Using such tools, students can try out hundreds of operating systems without dedicated hardware.
The advent of open-source operating systems has also made it easier to make the move from student to operating-system developer. With some knowledge, some effort, and an Internet connection, a student can even create a new operating-system distribution. Just a few years ago, it was difficult or impossible to get access to source code. Now, such access is limited only by how much interest, time, and disk space a student has.
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End of Chapter 1 Any question?
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