Operating Systems - Lecture 1 & 2 - PDF

Operating Systems ‫نظم تشغيل الحاسب‬ First Term 2023-2024 Dr. Reda Elbasiony 1  Chapter 1: Introduction Operating System Concepts – 10h Edition Silberschatz, Galvin and Gagne ©2018  Computer System Structure...

Operating Systems ‫نظم تشغيل الحاسب‬ First Term 2023-2024 Dr. Reda Elbasiony 1  Chapter 1: Introduction Operating System Concepts – 10h Edition Silberschatz, Galvin and Gagne ©2018  Computer System Structure Computer system can be divided into four components:  Hardware – provides basic computing resources  CPU, memory, I/O devices  Operating system  Controls 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  Word processors, compilers, web browsers, database systems, video games  Users  People, machines, other computers Operating System Concepts – 10th Edition 1.4 Silberschatz, Galvin and Gagne ©2018  Abstract View of Components of Computer Operating System Concepts – 10th Edition 1.5 Silberschatz, Galvin and Gagne ©2018  What Operating Systems Do Depends on the point of view Users want convenience, ease of use and good performance  Don’t care about resource utilization But shared computer such as mainframe or minicomputer must keep all users happy  Operating system is a resource allocator and control program making efficient use of HW and managing execution of user programs Users of dedicate systems such as workstations have dedicated resources but frequently use shared resources from servers Mobile devices like smartphones and tables are resource poor, optimized for usability and battery life Some computers have little or no user interface, such as embedded computers in devices and automobiles  Run primarily without user intervention Operating System Concepts – 10th Edition 1.6 Silberschatz, Galvin and Gagne ©2018  Operating System Definition No universally accepted definition “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’s OSes for general purpose and mobile computing also include middleware – a set of software frameworks that provide addition services to application developers such as databases, multimedia, graphics Operating System Concepts – 10th Edition 1.7 Silberschatz, Galvin and Gagne ©2018  Computer System Organization Computer-system operation  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 – 10th Edition 1.8 Silberschatz, Galvin and Gagne ©2018  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 Operating System Concepts – 10th Edition 1.9 Silberschatz, Galvin and Gagne ©2018  Common Functions of Interrupts 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 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 – 10th Edition 1.10 Silberschatz, Galvin and Gagne ©2018  Interrupt Timeline Operating System Concepts – 10th Edition 1.11 Silberschatz, Galvin and Gagne ©2018  Interrupt Handling The operating system preserves the state of the CPU by storing registers and the program counter Determines which type of interrupt has occurred: Separate segments of code determine what action should be taken for each type of interrupt Operating System Concepts – 10th Edition 1.13 Silberschatz, Galvin and Gagne ©2018  Interrupt-drive I/O Cycle Operating System Concepts – 10th Edition 1.14 Silberschatz, Galvin and Gagne ©2018  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 Operating System Concepts – 10th Edition 1.15 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 – 10th Edition 1.16 Silberschatz, Galvin and Gagne ©2018  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 Operating System Concepts – 10th Edition 1.17 Silberschatz, Galvin and Gagne ©2018  Storage-Device Hierarchy Operating System Concepts – 10th Edition 1.18 Silberschatz, Galvin and Gagne ©2018  How a Modern Computer Works A von Neumann architecture Operating System Concepts – 10th Edition 1.19 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 buffer storage directly to main memory without CPU intervention Only one interrupt is generated per block, rather than the one interrupt per byte Operating System Concepts – 10th Edition 1.20 Silberschatz, Galvin and Gagne ©2018  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 Operating System Concepts – 10th Edition 1.21 Silberschatz, Galvin and Gagne ©2018  Symmetric Multiprocessing Architecture Operating System Concepts – 10th Edition 1.22 Silberschatz, Galvin and Gagne ©2018  A Dual-Core Design Multi-chip and multicore Systems containing all chips  Chassis containing multiple separate systems Operating System Concepts – 10th Edition 1.23 Silberschatz, Galvin and Gagne ©2018  PC Motherboard Operating System Concepts – 10th Edition 1.24 Silberschatz, Galvin and Gagne ©2018  Operating-System Operations Bootstrap program – simple code to initialize the system, load the kernel Kernel loads 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):  Software error (e.g., division by zero)  Request for operating system service – system call  Other process problems include infinite loop, processes modifying each other or the operating system Operating System Concepts – 10th Edition 1.25 Silberschatz, Galvin and Gagne ©2018  Multiprogramming and Multitasking Multiprogramming (Batch system) needed for efficiency  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 memory Operating System Concepts – 10th Edition 1.26 Silberschatz, Galvin and Gagne ©2018  Memory Layout for Multiprogrammed System Operating System Concepts – 10th Edition 1.27 Silberschatz, Galvin and Gagne ©2018  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 hardware  Provides ability to distinguish when system is running user code or kernel code  Some instructions designated as privileged, only executable in kernel mode  System call changes mode to kernel, return from call resets it to user Increasingly CPUs support multi-mode operations Operating System Concepts – 10th Edition 1.28 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  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 time Operating System Concepts – 10th Edition 1.29 Silberschatz, Galvin and Gagne ©2018  Process Management A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. Process needs resources to accomplish its task  CPU, memory, I/O, files  Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute  Process executes instructions sequentially, one at a time, until completion Multi-threaded process has one program counter per thread Typically system has many processes, some user, some operating system running concurrently on one or more CPUs  Concurrency by multiplexing the CPUs among the processes / threads Operating System Concepts – 10th Edition 1.30 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 – 10th Edition 1.31 Silberschatz, Galvin and Gagne ©2018  Memory Management To execute a program all (or part) of the instructions must be in memory All (or part) of the data that is needed by the program must be in memory Memory management determines what is in memory and when  Optimizing CPU utilization and computer response to users Memory management activities  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 needed Operating System Concepts – 10th Edition 1.32 Silberschatz, Galvin and Gagne ©2018  File-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)  Varying 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 include  Creating and deleting files and directories  Primitives to manipulate files and directories  Mapping files onto secondary storage  Backup files onto stable (non-volatile) storage media Operating System Concepts – 10th Edition 1.33 Silberschatz, Galvin and Gagne ©2018  Mass-Storage Management Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities  Mounting and unmounting  Free-space management  Storage allocation  Disk scheduling  Partitioning  Protection Some storage need not be fast  Tertiary storage includes optical storage, magnetic tape  Still must be managed – by OS or applications Operating System Concepts – 10th Edition 1.34 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 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 policy Operating System Concepts – 10th Edition 1.35 Silberschatz, Galvin and Gagne ©2018  Characteristics of Various Types of Storage Movement between levels of storage hierarchy can be explicit or implicit Operating System Concepts – 10th Edition 1.36 Silberschatz, Galvin and Gagne ©2018  Migration of data “A” from Disk to Register Multitasking environments 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 Distributed environment situation even more complex  Several copies of a datum can exist  Various solutions covered in Chapter 19 Operating System Concepts – 10th Edition 1.37 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 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 rights Operating System Concepts – 10th Edition 1.38 Silberschatz, Galvin and Gagne ©2018  Computing Environments - Traditional Stand-alone general purpose machines 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 Operating System Concepts – 10th Edition 1.39 Silberschatz, Galvin and Gagne ©2018  Computing Environments - Mobile Handheld smartphones, tablets, etc What is the functional difference between them and a “traditional” laptop? Extra feature – more OS features (GPS, gyroscope) Allows new types of apps like augmented reality Use IEEE 802.11 wireless, or cellular data networks for connectivity Leaders are Apple iOS and Google Android Operating System Concepts – 10th Edition 1.40 Silberschatz, Galvin and Gagne ©2018  Computing Environments – Client-Server Client-Server Computing  Dumb terminals supplanted by smart PCs  Many systems now servers, responding to requests generated by clients  Compute-server system provides an interface to client to request services (i.e., database)  File-server system provides interface for clients to store and retrieve files Operating System Concepts – 10th Edition 1.41 Silberschatz, Galvin and Gagne ©2018  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 it 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) Operating System Concepts – 10th Edition 1.42 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 – 10th Edition 1.43 Silberschatz, Galvin and Gagne ©2018  End of Chapter 1 Operating System Concepts – 10h Edition Silberschatz, Galvin and Gagne ©2018