Module 1_Operating-System Services PDF

‫الجامعة السعودية االلكترونية‬ ‫الجامعة السعودية االلكترونية‬ ‫‪26/12/2021‬‬ College of Computing and Informatics OPERATING SYSTEMS  Module 1 Chapter 1: Introduction Chapter 2: Operating-System Services CONTENTS  What Operating System Do  Computer-System Organization, Arc...

‫الجامعة السعودية االلكترونية‬ ‫الجامعة السعودية االلكترونية‬ ‫‪26/12/2021‬‬ College of Computing and Informatics OPERATING SYSTEMS  Module 1 Chapter 1: Introduction Chapter 2: Operating-System Services CONTENTS  What Operating System Do  Computer-System Organization, Architecture and Operations  Resource Management  Virtualization  Computing Environments  Operating-System Services  User and Operating-System Interface  System Calls and Services Weekly LEARNING OUTCOMES  Describe computer system organization and role.  Define the components a computer system including multiprocessor computer systems.  Explain user and kernel mode transition.  Identify operating system services and system calls. WHAT IS AN OPERATING SYSTEM? An operating system is …… Is it only for Computers? How about these machines? Car Airplane Printer Washing Machine Toaster Compiler Etc.  WHAT OPERATING SYSTEM DO 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 By providing abstraction to application programs. Make the computer system convenient to use By turning ugly hardware into beautiful abstractions. Use the computer hardware in an efficient manner By orderly controlled allocation of resources. COMPUTER SYSTEM STRUCTURE Users (People, Machines, and other computers)  OPERATING SYSTEM DEFINITION 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’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  COMPUTER SYSTEM ORGANIZATION Computer-system consists of one or more CPUs, device controllers connect through common bus providing access to shared memory Operating systems (OS) have a device driver for each device controller which facilitate communication between OS and the device.  I/O OPERATION OVERVIEW A program request an I/O operation Device driver load appropriate registers in device controller The device controller, in turn, examines the contents of these registers to determine what action to take (such as “read a character from the keyboard”). The controller starts the transfer of data from the device to its local buffer. Once the transfer of data is complete, the device controller informs the device driver that it has finished its operation. The device driver then gives control to other parts of the operating system, possibly returning the data or a pointer to the data if the operation was a read. For other operations, the device driver returns status information such as “write completed successfully” or “device busy”. But how does the controller inform the device driver that it has finished its operation? This is accomplished via an interrupt.  INTERRUPT Hardware may trigger an interrupt at any time by sending a signal to the CPU, usually by way of the system bus. Interrupts are used for many other purposes as well and are a key part of how operating systems and hardware interact. Interrupts are an important part of a computer architecture. Each computer design has its own interrupt mechanism, but several functions are common. INTERRUPT  INTERRUPT HANDLING The operating system preserves the state of the CPU by storing the 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  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  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  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  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  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  STORAGE STRUCTURE (CONT.) 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  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 STORAGE-DEVICE HIERARCHY HOW A MODERN COMPUTER WORKS A von Neumann architecture  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 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  MULTIPROGRAMMING (BATCH SYSTEM) Single user cannot always keep CPU and I/O devices busy 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 job has to wait (for I/O for example), OS switches to another job  MULTITASKING (TIMESHARING) A logical extension of Batch systems– the 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  MULTITASKING (TIMESHARING) A logical extension of Batch systems– the 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 MEMORY LAYOUT FOR MULTIPROGRAMMED SYSTEM DUAL-MODE 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. When a user is running  mode bit is “user” When kernel code is executing  mode bit is “kernel” How do we guarantee that user does not explicitly set the mode bit to “kernel”? System call changes mode to kernel, return from call resets it to user Some instructions designated as privileged, only executable in kernel mode TRANSITION FROM USER TO KERNEL MODE TIMER Timer to prevent infinite loop (or 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 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 / 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 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 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 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 CHARACTERISTICS OF VARIOUS TYPES OF STORAGE Movement between levels of storage hierarchy can be explicit or implicit 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 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 VIRTUALIZATION Use cases involve laptops and desktops running multiple OSes for exploration or compatibility Apple laptop running Mac OS X host, Windows as a guest Developing apps for multiple OSes without having multiple systems Quality assurance 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 There is no general-purpose host then (VMware ESX and Citrix XenServer) VIRTUALIZATION (CONT.) Allows operating systems to run applications within other OSes 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 WinXP guests, each running applications, all on native WinXP host OS VMM (virtual machine Manager) provides virtualization services COMPUTING ENVIRONMENTS - VIRTUALIZATION 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: Increased throughput Economy of scale Increased reliability – graceful degradation or fault tolerance Two types: Asymmetric Multiprocessing – each processor is assigned a specie task. Symmetric Multiprocessing – each processor performs all tasks SYMMETRIC MULTIPROCESSING ARCHITECTURE DUAL-CORE DESIGN Multi-chip and multicore Systems containing all chips Chassis containing multiple separate systems COMPUTING ENVIRONMENTS Traditional Mobile Client Server Pear-to-Pear Cloud computing Real-time Embedded 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 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 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) CLOUD COMPUTING (CONT.) 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 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) Free software and open-source software are two different ideas championed by different groups of people https://www.gnu.org/philosophy/open-source-misses-the- point.en.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 OPERATING SYSTEM SERVICES Operating systems provide an environment for execution of programs and services to programs and users One set of operating-system services provides functions that are helpful to the user: User interface - Almost all operating systems have a user interface (UI). Varies between Command-Line (CLI), Graphics User Interface (GUI), touch- screen, Batch Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error) I/O operations - A running program may require I/O, which may involve a file or an I/O device File-system manipulation - The file system is of particular interest. Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management. OPERATING SYSTEM SERVICES (CONT.) One set of operating-system services provides functions that are helpful to the user (Cont.): Communications – Processes may exchange information, on the same computer or between computers over a network Communications may be via shared memory or through message passing (packets moved by the OS) Error detection – OS needs to be constantly aware of possible errors May occur in the CPU and memory hardware, in I/O devices, in user program For each type of error, OS should take the appropriate action to ensure correct and consistent computing Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system OPERATING SYSTEM SERVICES (CONT.) Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them Many types of resources - CPU cycles, main memory, file storage, I/O devices. Logging - To keep track of which users use how much and what kinds of computer resources Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other Protection involves ensuring that all access to system resources is controlled Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts A VIEW OF OPERATING SYSTEM SERVICES BOURNE SHELL COMMAND INTERPRETER USER OPERATING SYSTEM INTERFACE - GUI User-friendly desktop metaphor interface Usually mouse, keyboard, and monitor Icons represent files, programs, actions, etc Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder) Invented at Xerox PARC Many systems now include both CLI and GUI interfaces Microsoft Windows is GUI with CLI “command” shell Apple Mac OS X is “Aqua” GUI interface with UNIX kernel underneath and shells available Unix and Linux have CLI with optional GUI interfaces TOUCHSCREEN INTERFACES Touchscreen devices require new interfaces Mouse not possible or not desired Actions and selection based on gestures Virtual keyboard for text entry Voice commands THE MAC OS X GUI SYSTEM CALLS Programming interface to the services provided by the OS Typically written in a high-level language (C or C++) Mostly accessed by programs via a high-level Application Programming Interface (API) rather than direct system call use Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM) EXAMPLE OF SYSTEM CALLS System call sequence to copy the contents of one file to another file EXAMPLE OF STANDARD API SYSTEM CALL IMPLEMENTATION Typically, a number is associated with each system call System-call interface maintains a table indexed according to these numbers The system call interface invokes the intended system call in OS kernel and returns status of the system call and any return values The caller need know nothing about how the system call is implemented Just needs to obey API and understand what OS will do as a result call Most details of OS interface hidden from programmer by API Managed by run-time support library (set of functions SYSTEM CALL PARAMETER PASSING Often, more information is required than simply identity of desired system call Exact type and amount of information vary according to OS and call Three general methods used to pass parameters to the OS Simplest: pass the parameters in registers In some cases, may be more parameters than registers Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register This approach taken by Linux and Solaris Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system Block and stack methods do not limit the number or length of parameters being passed PARAMETER PASSING VIA TABLE TYPES OF SYSTEM CALLS Process control create process, terminate process end, abort load, execute get process attributes, set process attributes wait for time wait event, signal event allocate and free memory Dump memory if error Debugger for determining bugs, single step execution Locks for managing access to shared data between processes TYPES OF SYSTEM CALLS (CONT.) File management create file, delete file open, close file read, write, reposition get and set file attributes Device management request device, release device read, write, reposition get device attributes, set device attributes logically attach or detach devices TYPES OF SYSTEM CALLS (CONT.) Information maintenance get time or date, set time or date get system data, set system data get and set process, file, or device attributes Communications create, delete communication connection send, receive messages if message passing model to host name or process name From client to server Shared-memory model create and gain access to memory regions TYPES OF SYSTEM CALLS (CONT.) Protection Control access to resources Get and set permissions Allow and deny user access EXAMPLES OF WINDOWS AND UNIX SYSTEM CALLS SYSTEM SERVICES 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 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 SYSTEM SERVICES (CONT.) 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 SYSTEM SERVICES (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 SYSTEM SERVICES (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 WHY APPLICATIONS ARE OPERATING SYSTEM SPECIFIC Apps compiled on one system usually not executable on other operating systems Each operating system provides its own unique system calls Own file formats, etc. Apps can be multi-operating system Written in interpreted language like Python, Ruby, and interpreter available on multiple operating systems App written in language that includes a VM containing the running app (like Java) Use standard language (like C), compile separately on each operating system to run on each Application Binary Interface (ABI) is architecture equivalent of API, defines how different components of binary code can interface for a given operating system on a given architecture, CPU, etc.  Required Reading 1. Chapter 1: Introduction (Operating System Concepts by Silberschatz, Abraham, et al. 10th ed., ISBN: 978- 1-119-32091-3, 2018) 2. Chapter 2: Operating-System Structures (Operating System Concepts by Silberschatz, Abraham, et al. 10th ed., ISBN: 978-1-119-32091-3, 2018) Recommended Reading 1. Chapter 1 (Modern Operating Systems by Andrew S. Tanenbaum and Herbert Bos. 4th ed., ISBN-10: 0-13- 359162-X, ISBN-13: 978-0-13-359162-0, 2015) tation is mainly dependent on the textbook: Operating System Concepts by Silberschatz, Abraham, et al. 1 Thank You