Computer Operating System - Chapter 1: Introduction

Term OS covers many roles
Because of myriad designs and uses of OSes
OSes present in toasters through ships, spacecraft, game machines, TVs
and industrial control systems
OSes were born when fixed use of computers for military became more
general purpose and needed resource management and program control
No universally accepted definition

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Course Syllabus Credits 3 Code CO2017 Total: Lecture: Lab: Assignment: Credits Hours 60 30 14 X Exercise: Lab: Midterm: Assignment: Final exam: Evaluation 10% 10% 30% 50% Assessment method Final exam: Multiple choice questions, ~ 90 minutes Prerequisites Co-requisites Undergraduate Computer Science and Computer Engineering Programs Website Operating System Concepts 2 Silberschatz, Galvin and Gagne ©2018
Course Outline Introduction to Operating systems Security and protection Processes/Threads management Advanced topics CPU scheduling Summary Synchronization Memory management Main memory Virtual memory I/O management Storage management File systems Operating System Concepts 4 Silberschatz, Galvin and Gagne ©2018
Objectives Describe the general organization of a computer system and the role of interrupts Describe the components in a modern, multiprocessor computer system Illustrate the transition from user mode to kernel mode Discuss how operating systems are used in various computing environments Provide examples of free and open-source operating systems Operating System Concepts 8 Silberschatz, Galvin and Gagne ©2018
Defining Operating Systems Term OS covers many roles Because of myriad designs and uses of OSes OSes present in toasters through ships, spacecraft, game machines, TVs and industrial control systems OSes were born when fixed use of computers for military became more general purpose and needed resource management and program control No universally accepted definition Operating System Concepts 12 Silberschatz, Galvin and Gagne ©2018
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 Operating System Concepts 14 Silberschatz, Galvin and Gagne ©2018
Common Functions of Interrupts Device controller informs CPU that it has finished its operation by raising an interrupt or CPU has to do a polling for an I/O completion (possibly waste a large number of CPU cycles) Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines Interrupt architecture must save the address and status of the interrupted instruction A trap (or exception) is a software-generated interrupt caused either by an error or a user request An operating system is interrupt-driven Operating System Concepts 16 Silberschatz, Galvin and Gagne ©2018
Interrupt Handling The operating system preserves the state of the CPU by storing registers and the program counter (PC) Determines which type of interrupt has occurred: Vectored interrupt system used to handle asynchronous events and to trap to supervisor-mode routines in the kernel Separate segments of code determine what action should be taken for each type of interrupt Some device drivers use interrupts when the I/O rate is low and switch to polling when the rate increases to the point where polling is faster and more efficient. Operating System Concepts 18 Silberschatz, Galvin and Gagne ©2018
I/O Structure After I/O starts, control returns to user program only upon I/O completion Wait instruction idles the CPU until the next interrupt Wait loop (e.g., contention for memory access) At most one I/O request is outstanding at a time, no simultaneous I/O processing After I/O starts, control returns to user program without waiting for I/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 Operating System Concepts 20 Silberschatz, Galvin and Gagne ©2018
Storage Definitions and Notation Review 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). Operating System Concepts 22 Silberschatz, Galvin and Gagne ©2018
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 local buffer directly to main memory without CPU intervention Only one interrupt is generated per block, rather than the one interrupt per byte Operating System Concepts 26 Silberschatz, Galvin and Gagne ©2018
Non-Uniform Memory Access System Non-Uniform Memory Access (NUMA) Operating System Concepts 30 Silberschatz, Galvin and Gagne ©2018
Multiprogramming Multiprogramming needed for efficiency Single user cannot keep CPU and I/O devices busy at all times Multiprogramming organizes jobs (i.e., code and data) so that CPU always has one to execute A subset of total jobs in system is kept in memory One job is selected and runs via job scheduling When it has to wait (e.g., for I/O), OS switches to another job Operating System Concepts 34 Silberschatz, Galvin and Gagne ©2018
Transition from User to Kernel Mode Timer to prevent infinite loop / process hogging resources Timer is set to interrupt the computer after some time period. Operating system sets a counter (privileged instruction), keeps the counter that is decremented by the physical clock, when counter zero generate an interrupt. Set up before scheduling process to regain control or terminate program that exceeds allotted time. Operating System Concepts 38 Silberschatz, Galvin and Gagne ©2018
Process Management Activities The operating system is responsible for the following activities in connection 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 handling Operating System Concepts 40 Silberschatz, Galvin and Gagne ©2018
Filesystem Management OS provides uniform, logical view of data storage Abstracts physical properties to logical storage unit - file Each medium is controlled by device (i.e., disk drive, tape drive)  Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random) Filesystem management Files usually organized into directories Access control on most systems to determine who can access what OS activities Creating and deleting files / directories, primitives to manipulate files / directories, to backup files onto stable (non-volatile) storage media Mapping files onto secondary storage Operating System Concepts 42 Silberschatz, Galvin and Gagne ©2018
Caching 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 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 is smaller than storage being cached Cache management is an important design problem Cache size and replacement policy Operating System Concepts 44 Silberschatz, Galvin and Gagne ©2018
Migration of Data from Disk to Register Multitasking environment must be careful to use most recent value, no matter where it is stored in the storage hierarchy Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache In distributed environment, the situation is even more complex Several copies of a datum can exist Various solutions Operating System Concepts 46 Silberschatz, Galvin and Gagne ©2018
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 identity (UID, or security ID) includes name and an associated number. User ID is then associated with all files, processes of that user to determine access control  Group identifier (GID) allows set of users to be defined for access control, then also associated with each process or file  Privilege escalation allows user to change to effective ID with more rights Operating System Concepts 48 Silberschatz, Galvin and Gagne ©2018
Virtualization (cont.) Use cases involve laptops and desktops running multiple OSes for exploration or compatibility E.g.,  Apple laptop running Mac OS X host, Windows as a guest  Developing apps for multiple OSes without having multiple systems  Q&A testing applications without having multiple systems  Executing and managing computing environments within data centers VMM can run natively, in which case they are also the host There is no general purpose host then (e.g., VMware ESX and Citrix XenServer) Operating System Concepts 50 Silberschatz, Galvin and Gagne ©2018
Distributed Systems Distributed computing Collection of separate (possibly heterogeneous) systems networked together  Network is communications paths (TCP/IP is most common protocol stack) – Local Area Network (LAN) – Wide Area Network (WAN) – Metropolitan Area Network (MAN) – Personal Area Network (PAN) Network Operating System (NOS) provides features between systems across network  Communication scheme allows systems to exchange messages  Illusion of a single system Operating System Concepts 52 Silberschatz, Galvin and Gagne ©2018
Kernel Data Structures Binary search tree (left <= right) Search performance is O(n) Balanced binary search tree is O(log n) Operating System Concepts 54 Silberschatz, Galvin and Gagne ©2018
Evolution Mainframe system Desktop system Multiprocessor system Distributed system Real-time system Handheld system/mobile system Operating System Concepts 56 Silberschatz, Galvin and Gagne ©2018
Computing Environments - Mobile Such as handheld smartphones, tablets, etc. What is the functional difference between them and a “traditional” laptop? Extra feature – more OS features (e.g., GPS, gyroscope) Allows new types of apps like Augmented Reality (AR) Use IEEE 802.11 wireless, or cellular data networks for connectivity Leaders are Apple iOS and Google Android Operating System Concepts 58 Silberschatz, Galvin and Gagne ©2018
Computing Environments - Peer-to-Peer Another model of distributed system 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  Registers its service with central lookup service on network, or  Broadcast request for service and respond to requests for service via discovery protocol Examples include Napster and Gnutella, Voice over IP (VoIP) such as Skype Operating System Concepts 60 Silberschatz, Galvin and Gagne ©2018
Computing Environments – Cloud Computing Cloud computing environments composed of traditional OSes, plus VMMs, plus cloud management tools Internet connectivity requires security like firewalls Load balancers spread traffic across multiple applications Operating System Concepts 62 Silberschatz, Galvin and Gagne ©2018
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 Started by Free Software Foundation (FSF), which has “copyleft” GNU Public License (GPL) or Lesser GPL (LGPL) Free software and open-source software are two different ideas championed by different groups of people  E.g., GNU/Linux and BSD UNIX (including Darwin, core of Mac OS X) Use VMM like VMware Player (Free on Windows), VirtualBox Use to run guest operating systems for exploration Operating System Concepts 64 Silberschatz, Galvin and Gagne ©2018
Summary An operating system is software that manages the computer hardware, as well as providing an environment for application programs to run. Interrupts are a key way in which hardware interacts with the operating system. A hardware device triggers an interrupt by sending a signal to the CPU to alert the CPU that some event requires attention. The interrupt is managed by the interrupt handler. For a computer to do its job of executing programs, the programs must be in main memory, which is the only large storage area that the processor can access directly. The main memory is usually a volatile storage device that loses its contents when power is turned off or lost. Operating System Concepts 66 Silberschatz, Galvin and Gagne ©2018
Summary (Cont.) To best utilize the CPU, modern operating systems employ multiprogramming, which allows several jobs to be in memory at the same time, thus ensuring that the CPU always has a job to execute. Multitasking is an extension of multiprogramming wherein CPU scheduling algorithms rapidly switch between processes, providing users with a fast response time. To prevent user programs from interfering with the proper operation of the system, the system hardware has two modes: user mode and kernel mode. Various instructions are privileged and can be executed only in kernel mode. Examples include the instruction to switch to kernel mode, I/O control, timer management, and interrupt management. Operating System Concepts 68 Silberschatz, Galvin and Gagne ©2018
Summary (Cont.) Virtualization involves abstracting a computer’s hardware into several different execution environments. Data structures that are used in an operating system include lists, stacks, queues, trees, and maps. Computing takes place in a variety of environments, including traditional computing, mobile computing, client-server systems, peer- to-peer systems, cloud computing, and real-time embedded systems. Free and open-source operating systems are available in source- code format. Free software is licensed to allow no-cost use, redistribution, and modification. GNU/Linux, FreeBSD, and Solaris are examples of popular open-source systems. Operating System Concepts 70 Silberschatz, Galvin and Gagne ©2018