UNIT 1-21CSC202J- Operating System.ppt.pdf

21CSC202J Operating Systems UNIT I  Introduction What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Process Management Memory M...

21CSC202J Operating Systems UNIT I  Introduction What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Process Management Memory Management Storage Management Protection and Security Kernel Data Structures Computing Environments Open-Source Operating Systems 21CSC202J Operating Systems * 2 UNIT 1  Objectives To describe the basic organization of computer systems To provide a grand tour of the major components of operating systems To give an overview of the many types of computing environments To explore several open-source operating systems 21CSC202J Operating Systems * 3 UNIT 1  What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware Operating system goals: – Execute user programs and make solving user problems easier – Make the computer system convenient to use – Use the computer hardware in an efficient manner 21CSC202J Operating Systems * 4 UNIT 1  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 21CSC202J Operating Systems * 5 UNIT 1  Four Components of a Computer System 21CSC202J Operating Systems * 6 UNIT 1  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 Users of dedicate systems such as workstations have dedicated resources but frequently use shared resources from servers Handheld computers 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 21CSC202J Operating Systems * 7 UNIT 1  Operating System Definition OS is a resource allocator – Manages all resources – Decides between conflicting requests for efficient and fair resource use OS is a control program – Controls execution of programs to prevent errors and improper use of the computer 21CSC202J Operating Systems * 8 UNIT 1  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. Everything else is either – a system program (ships with the operating system) , or – an application program. 21CSC202J Operating Systems * 9 UNIT 1  Computer Startup 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 21CSC202J Operating Systems * 10 UNIT 1  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 21CSC202J Operating Systems * 11 UNIT 1  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 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 21CSC202J Operating Systems * 12 UNIT 1  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 21CSC202J Operating Systems * 13 UNIT 1  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: – polling – vectored interrupt system Separate segments of code determine what action should be taken for each type of interrupt 21CSC202J Operating Systems * 14 UNIT 1  Interrupt Timeline 21CSC202J Operating Systems * 15 UNIT 1  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 (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 21CSC202J Operating Systems * 16 UNIT 1  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 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). 21CSC202J Operating Systems * 17 UNIT 1  Storage Structure Main memory – only large storage media that the CPU can access directly – Random access – Typically volatile Secondary storage – extension of main memory that provides large nonvolatile storage capacity Hard disks – 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 Solid-state disks – faster than hard disks, nonvolatile – Various technologies – Becoming more popular 21CSC202J Operating Systems * 18 UNIT 1  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 21CSC202J Operating Systems * 19 UNIT 1  Storage-Device Hierarchy 21CSC202J Operating Systems * 20 UNIT 1  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 21CSC202J Operating Systems * 21 UNIT 1  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 21CSC202J Operating Systems * 22 UNIT 1  How a Modern Computer Works A von Neumann architecture 21CSC202J Operating Systems * 23 UNIT 1  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 21CSC202J Operating Systems * 24 UNIT 1  Symmetric Multiprocessing Architecture 21CSC202J Operating Systems * 25 UNIT 1  A Dual-Core Design Multi-chip and multicore Systems containing all chips – Chassis containing multiple separate systems 21CSC202J Operating Systems * 26 UNIT 1  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 Asymmetric clustering has one machine in hot-standby mode Symmetric clustering has multiple nodes running applications, monitoring each other – Some clusters are for high-performance computing (HPC) Applications must be written to use parallelization – Some have distributed lock manager (DLM) to avoid conflicting operations 21CSC202J Operating Systems * 27 UNIT 1  Clustered Systems 21CSC202J Operating Systems * 28 UNIT 1  Operating System Structure 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 21CSC202J Operating Systems * 29 UNIT 1  Memory Layout for Multiprogrammed System 21CSC202J Operating Systems * 30 UNIT 1  Operating-System Operations 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 Other process problems include infinite loop, processes modifying each other or the operating system 21CSC202J Operating Systems * 31 UNIT 1  Operating-System Operations (cont.) 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 – i.e. virtual machine manager (VMM) mode for guest VMs 21CSC202J Operating Systems * 32 UNIT 1  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 21CSC202J Operating Systems * 33 UNIT 1  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 21CSC202J Operating Systems * 34 UNIT 1  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 21CSC202J Operating Systems * 35 UNIT 1  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 21CSC202J Operating Systems * 36 UNIT 1  Storage 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 21CSC202J Operating Systems * 37 UNIT 1  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 – Free-space management – Storage allocation – Disk scheduling Some storage need not be fast – Tertiary storage includes optical storage, magnetic tape – Still must be managed – by OS or applications – Varies between WORM (write-once, read-many-times) and RW * (read-write) 21CSC202J Operating Systems 38 UNIT 1  Performance of Various Levels of Storage Movement between levels of storage hierarchy can be explicit or implicit 21CSC202J Operating Systems * 39 UNIT 1  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 21CSC202J Operating Systems * 40 UNIT 1  I/O Subsystem One purpose of OS is to hide peculiarities of hardware devices from the user I/O subsystem responsible for – Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs) – General device-driver interface – Drivers for specific hardware devices 21CSC202J Operating Systems * 41 UNIT 1  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 21CSC202J Operating Systems UNIT 1 42  Kernel Data Structures Many similar to standard programming data structures Singly linked list Doubly linked list Circular linked list 21CSC202J Operating Systems * 43 UNIT 1  Kernel Data Structures Binary search tree left shell reloaded At system startup running a program 21CSC202J Operating Systems * 82 UNIT 1  Example: FreeBSD Unix variant Multitasking User login -> invoke user’s choice of shell Shell executes fork() system call to create process – Executes exec() to load program into process – Shell waits for process to terminate or continues with user commands Process exits with: – code = 0 – no error – code > 0 – error code 21CSC202J Operating Systems * 83 UNIT 1  System Programs System programs provide a convenient environment for program development and execution. They can be divided into: – File manipulation – Status information sometimes stored in a File modification – Programming language support – Program loading and execution – Communications – Background services – Application programs Most users’ view of the operation system is defined by system programs, not the actual system calls 21CSC202J Operating Systems * 84 UNIT 1  System Programs Provide a convenient environment for program development and execution – Some of them are simply user interfaces to system calls; others are considerably more complex File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories Status information – Some ask the system for info - date, time, amount of available memory, disk space, number of users – Others provide detailed performance, logging, and debugging information – Typically, these programs format and print the output to the terminal or other output devices – Some systems implement a registry - used to store and retrieve configuration information 21CSC202J Operating Systems * 85 UNIT 1  System Programs (Cont.) File modification – Text editors to create and modify files – Special commands to search contents of files or perform transformations of the text Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided Program loading and execution- Absolute loaders, relocatable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems – Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another 21CSC202J Operating Systems * 86 UNIT 1  System Programs (Cont.) Background Services – Launch at boot time Some for system startup, then terminate Some from system boot to shutdown – Provide facilities like disk checking, process scheduling, error logging, printing – Run in user context not kernel context – Known as services, subsystems, daemons Application programs – Don’t pertain to system – Run by users – Not typically considered part of OS – Launched by command line, mouse click, finger poke 21CSC202J Operating Systems * 87 UNIT 1  Operating System Design and Implementation Design and Implementation of OS not “solvable”, but some approaches have proven successful Internal structure of different Operating Systems can vary widely Start the design by defining goals and specifications Affected by choice of hardware, type of system User goals and System goals – User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast – System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient 21CSC202J Operating Systems * 88 UNIT 1  Operating System Design and Implementation (Cont.) Important principle to separate Policy: What will be done? Mechanism: How to do it? Mechanisms determine how to do something, policies decide what will be done The separation of policy from mechanism is a very important principle, it allows maximum flexibility if policy decisions are to be changed later (example – timer) Specifying and designing an OS is highly creative task of software engineering 21CSC202J Operating Systems * 89 UNIT 1  Implementation Much variation – Early OSes in assembly language – Then system programming languages like Algol, PL/1 – Now C, C++ Actually usually a mix of languages – Lowest levels in assembly – Main body in C – Systems programs in C, C++, scripting languages like PERL, Python, shell scripts More high-level language easier to port to other hardware – But slower Emulation can allow an OS to run on non-native hardware 21CSC202J Operating Systems * 90 UNIT 1  Operating System Structure General-purpose OS is very large program Various ways to structure ones – Simple structure – MS-DOS – More complex -- UNIX – Layered – an abstrcation – Microkernel -Mach 21CSC202J Operating Systems * 91 UNIT 1  Simple Structure -- MS-DOS MS-DOS – written to provide the most functionality in the least space – Not divided into modules – Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated 21CSC202J Operating Systems * 92 UNIT 1  Non Simple Structure -- UNIX UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts – Systems programs – The kernel Consists of everything below the system-call interface and above the physical hardware Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level 21CSC202J Operating Systems * 93 UNIT 1  Traditional UNIX System Structure Beyond simple but not fully layered 21CSC202J Operating Systems * 94 UNIT 1  Layered Approach The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers 21CSC202J Operating Systems * 95 UNIT 1  Microkernel System Structure Moves as much from the kernel into user space Mach example of microkernel – Mac OS X kernel (Darwin) partly based on Mach Communication takes place between user modules using message passing Benefits: – Easier to extend a microkernel – Easier to port the operating system to new architectures – More reliable (less code is running in kernel mode) – More secure Detriments: – Performance overhead of user space to kernel space communication 21CSC202J Operating Systems * 96 UNIT 1  Microkernel System Structure 21CSC202J Operating Systems * 97 UNIT 1  Modules Many modern operating systems implement loadable kernel modules – Uses object-oriented approach – Each core component is separate – Each talks to the others over known interfaces – Each is loadable as needed within the kernel Overall, similar to layers but with more flexible – Linux, Solaris, etc 21CSC202J Operating Systems * 98 UNIT 1  Solaris Modular Approach 21CSC202J Operating Systems * 99 UNIT 1  Hybrid Systems Most modern operating systems are actually not one pure model – Hybrid combines multiple approaches to address performance, security, usability needs – Linux and Solaris kernels in kernel address space, so monolithic, plus modular for dynamic loading of functionality – Windows mostly monolithic, plus microkernel for different subsystem personalities Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa programming environment – Below is kernel consisting of Mach microkernel and BSD Unix parts, plus I/O kit and dynamically loadable modules (called kernel extensions) 21CSC202J Operating Systems * 100 UNIT 1  Mac OS X Structure 21CSC202J Operating Systems * 101 UNIT 1  iOS Apple mobile OS for iPhone, iPad – Structured on Mac OS X, added functionality – Does not run OS X applications natively Also runs on different CPU architecture (ARM vs. Intel) – Cocoa Touch Objective-C API for developing apps – Media services layer for graphics, audio, video – Core services provides cloud computing, databases – Core operating system, based on Mac OS X kernel 21CSC202J Operating Systems * 102 UNIT 1  Android Developed by Open Handset Alliance (mostly Google) – Open Source Similar stack to IOS Based on Linux kernel but modified – Provides process, memory, device-driver management – Adds power management Runtime environment includes core set of libraries and Dalvik virtual machine – Apps developed in Java plus Android API Java class files compiled to Java bytecode then translated to executable than runs in Dalvik VM Libraries include frameworks for web browser (webkit), database (SQLite), multimedia, smaller libc 21CSC202J Operating Systems * 103 UNIT 1  Android Architecture 21CSC202J Operating Systems * 104 UNIT 1  Operating-System Debugging Debugging is finding and fixing errors, or bugs OS generate log files containing error information Failure of an application can generate core dump file capturing memory of the process Operating system failure can generate crash dump file containing kernel memory Beyond crashes, performance tuning can optimize system performance – Sometimes using trace listings of activities, recorded for analysis – Profiling is periodic sampling of instruction pointer to look for statistical trends Kernighan’s Law: “Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.” 21CSC202J Operating Systems * 105 UNIT 1  Performance Tuning Improve performance by removing bottlenecks OS must provide means of computing and displaying measures of system behavior For example, “top” program or Windows Task Manager 21CSC202J Operating Systems * 106 UNIT 1  DTrace DTrace tool in Solaris, FreeBSD, Mac OS X allows live instrumentation on production systems Probes fire when code is executed within a provider, capturing state data and sending it to consumers of those probes Example of following XEventsQueued system call move from libc library to kernel and back 21CSC202J Operating Systems * 107 UNIT 1  Dtrace (Cont.) DTrace code to record amount of time each process with UserID 101 is in running mode (on CPU) in nanoseconds 21CSC202J Operating Systems * 108 UNIT 1  Operating System Generation Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site SYSGEN program obtains information concerning the specific configuration of the hardware system Used to build system-specific compiled kernel or system-tuned Can general more efficient code than one general kernel 21CSC202J Operating Systems * 109 UNIT 1  System Boot When power initialized on system, execution starts at a fixed memory location – Firmware ROM used to hold initial boot code Operating system must be made available to hardware so hardware can start it – Small piece of code – bootstrap loader, stored in ROM or EEPROM locates the kernel, loads it into memory, and starts it – Sometimes two-step process where boot block at fixed location loaded by ROM code, which loads bootstrap loader from disk Common bootstrap loader, GRUB, allows selection of kernel from multiple disks, versions, kernel options 110 Kernel loads and system is then running 21CSC202J Operating Systems * 110 UNIT 1