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CS 571 Operating Systems Prof. Sanjeev Setia Fall 2001 Overview ? Prerequisites ? Computer Architecture (CS 365) ? C++/C/Java progamming ? Textbook ? Silbershatz,Galvin,Gagne – Operating Systems Concepts ? Grading ? One midterm exam (25%), Final Exam (25%) ? Assignments (50%) ? Three Programming Assignments ? Concurrent Programming ? RPC/RMI ? Distributed File System ? First two to be done individually, third may be done in groups of two ? Late submission penalty – 10% per day ? Can “redo”first two assignments to improve grade to some extent (can make up half the difference between old grade and max grade) Operating Systems 1.2 1 Logistics ? Class Web Page ? http://www.cs.gmu.edu/~setia/cs571/ ? Slides, Handouts, Old Exams, Useful Links ? Slides ? More than 90% of slides taken from slides made available by authors of textbook ? http://www.bell-labs.com/topic/books/os-book/ ? Office Hrs ? Monday, 2 – 4 pm, Room 347, S&T II ? [email protected] ? TA ? Vamshi Kalakuntla ? Office Hrs ? Office ? Computer Accounts (IT&E or your own machine at home/work) Operating Systems 1.3 Chapter 1: Introduction ? What is an Operating System? ? Mainframe Systems ? Desktop Systems ? Multiprocessor Systems ? Distributed Systems ? Clustered System ? Real -Time Systems ? Handheld Systems ? Computing Environments Operating Systems 1.4 2 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. Operating Systems 1.5 Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers). Operating Systems 1.6 3 Abstract View of System Components Operating Systems 1.7 Operating System Definitions ? Resource allocator – manages and allocates resources. ? Control program – controls the execution of user programs and operations of I/O devices . ? Kernel – the one program running at all times (all else being application programs). Operating Systems 1.8 4 Mainframe Systems ? Reduce setup time by batching similar jobs ? Automatic job sequencing – automatically transfers control from one job to another. First rudimentary operating system. ? Resident monitor ? initial control in monitor ? control transfers to job ? when job completes control transfers pack to monitor Operating Systems 1.9 Memory Layout for a Simple Batch System Operating Systems 1.10 5 Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. Operating Systems 1.11 OS Features Needed for Multiprogramming ? I/O routine supplied by the system. ? Memory management – the system must allocate the memory to several jobs. ? CPU scheduling – the system must choose among several jobs ready to run. ? Allocation of devices. Operating Systems 1.12 6 Time-Sharing Systems–Interactive Computing ? The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). ? A job swapped in and out of memory to the disk. ? On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement”from the user’s keyboard. ? On-line system must be available for users to access data and code. Operating Systems 1.13 Desktop Systems ? Personal computers – computer system dedicated to a single user. ? I/O devices – keyboards, mice, display screens, small printers. ? User convenience and responsiveness. ? Can adopt technology developed for larger operating system’often individuals have sole use of computer and do not need advanced CPU utilization of protection features. ? May run several different types of operating systems (Windows, MacOS, UNIX, Linux) Operating Systems 1.14 7 Parallel Systems ? Multiprocessor systems with more than on CPU in close communication. ? Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. ? Advantages of parallel system: ? Increased throughput ? Economical ? Increased reliability ? graceful degradation ? fail-soft systems Operating Systems 1.15 Parallel Systems (Cont.) ? Symmetric multiprocessing (SMP) ? Each processor runs and identical copy of the operating system. ? Many processes can run at once without performance deterioration. ? Most modern operating systems support SMP ? Asymmetric multiprocessing ? Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. ? More common in extremely large systems Operating Systems 1.16 8 Symmetric Multiprocessing Architecture Operating Systems 1.17 Distributed Systems ? Distribute the computation among several physical processors. ? Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as highspeed buses or telephone lines. ? Advantages of distributed systems. ? Resources Sharing ? Computation speed up – load sharing ? Reliability ? Communications Operating Systems 1.18 9 Distributed Systems (cont) ? Requires networking infrastructure. ? Local area networks (LAN) or Wide area networks (WAN) ? May be either client-server or peer-to-peer systems. Operating Systems 1.19 General Structure of Client-Server Operating Systems 1.20 10 Clustered Systems ? Clustering allows two or more systems to share storage. ? Provides high reliability. ? Asymmetric clustering: one server runs the application while other servers standby. ? Symmetric clustering: all N hosts are running the application. Operating Systems 1.21 Real-Time Systems ? Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. ? Well-defined fixed-time constraints. ? Real-Time systems may be either hard or soft real-time. Operating Systems 1.22 11 Real-Time Systems (Cont.) ? Hard real-time: ? Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM) ? Conflicts with time-sharing systems, not supported by general-purpose operating systems. ? Soft real-time ? Limited utility in industrial control of robotics ? Useful in applications (multimedia, virtual reality) requiring advanced operating-system features. Operating Systems 1.23 Handheld Systems ? Personal Digital Assistants (PDAs) ? Cellular telephones ? Issues: ? Limited memory ? Slow processors ? Small display screens. Operating Systems 1.24 12 Migration of Operating-System Concepts and Features Operating Systems 1.25 Chapter 2: Computer-System Structures ? Computer System Operation ? I/O Structure ? Storage Structure ? Storage Hierarchy ? Hardware Protection ? General System Architecture Operating Systems 1.26 13 Computer-System Architecture Operating Systems 1.27 Computer-System Operation ? I/O devices and the CPU can execute concurrently. ? Each device controller is in charge of a particular device ? ? ? ? Operating Systems 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. 1.28 14 Common Functions of Interrupts ? Interrupt transfers control to the interrupt service routine ? ? ? ? Operating Systems generally, through the interrupt vector, which contains the addresses of all the service routines. Interrupt architecture must save the address of the interrupted instruction. Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt. A trap is a software-generated interrupt caused either by an error or a user request. An operating system is interrupt driven. 1.29 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 Operating Systems 1.30 15 Interrupt Time Line For a Single Process Doing Output Operating Systems 1.31 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 operating system 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. ? Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt. Operating Systems 1.32 16 Two I/O Methods Synchronous Operating Systems Asynchronous 1.33 Device-Status Table Operating Systems 1.34 17 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 on interrupt is generated per block, rather than the one interrupt per byte. Operating Systems 1.35 Storage Structure ? Main memory – only large storage media that the CPU can access directly. ? Secondary storage – extension of main memory that provides large nonvolatile storage capacity. ? Magnetic 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. Operating Systems 1.36 18 Moving-Head Disk Mechanism Operating Systems 1.37 Storage Hierarchy ? Storage systems organized in hierarchy. ? Speed ? Cost ? Volatility ? Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage. Operating Systems 1.38 19 Storage-Device Hierarchy Operating Systems 1.39 Caching ? Use of high-speed memory to hold recently-accessed data. ? Requires a cache management policy. ? Caching introduces another level in storage hierarchy. This requires data that is simultaneously stored in more than one level to be consistent. Operating Systems 1.40 20 Migration of A From Disk to Register Operating Systems 1.41 Hardware Protection ? Dual-Mode Operation ? I/O Protection ? Memory Protection ? CPU Protection Operating Systems 1.42 21 Dual-Mode Operation ? Sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly. ? Provide hardware support to differentiate between at least two modes of operations. 1. User mode – execution done on behalf of a user. 2. Monitor mode (also kernel mode or system mode) – execution done on behalf of operating system. Operating Systems 1.43 Dual-Mode Operation (Cont.) ? Mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1). ? When an interrupt or fault occurs hardware switches to monitor mode. Interrupt/fault monitor user set user mode Privileged instructions can be issued only in monitor mode. Operating Systems 1.44 22 I/O Protection ? All I/O instructions are privileged instructions. ? Must ensure that a user program could never gain control of the computer in monitor mode (I.e., a user program that, as part of its execution, stores a new address in the interrupt vector). Operating Systems 1.45 Use of A System Call to Perform I/O Operating Systems 1.46 23 Memory Protection ? Must provide memory protection at least for the interrupt vector and the interrupt service routines. ? In order to have memory protection, add two registers that determine the range of legal addresses a program may access: ? Base register – holds the smallest legal physical memory address. ? Limit register – contains the size of the range ? Memory outside the defined range is protected. Operating Systems 1.47 Use of A Base and Limit Register Operating Systems 1.48 24 Hardware Address Protection Operating Systems 1.49 Hardware Protection ? When executing in monitor mode, the operating system has unrestricted access to both monitor and user’s memory. ? The load instructions for the base and limit registers are privileged instructions. Operating Systems 1.50 25 CPU Protection ? Timer – interrupts computer after specified period to ensure operating system maintains control. ? Timer is decremented every clock tick. ? When timer reaches the value 0, an interrupt occurs. ? Timer commonly used to implement time sharing. ? Time also used to compute the current time. ? Load-timer is a privileged instruction. Operating Systems 1.51 Network Structure ? Local Area Networks (LAN) ? Wide Area Networks (WAN) Operating Systems 1.52 26 Local Area Network Structure Operating Systems 1.53 Wide Area Network Structure Operating Systems 1.54 27 Chapter 3: Operating-System Structures ? System Components ? Operating System Services ? System Calls ? System Programs ? System Structure ? Virtual Machines ? System Design and Implementation ? System Generation Operating Systems 1.55 Common System Components ? Process Management ? Main Memory Management ? File Management ? I/O System Management ? Secondary Management ? Networking ? Protection System ? Command-Interpreter System Operating Systems 1.56 28 Process Management ? A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task. ? The operating system is responsible for the following activities in connection with process management. ? Process creation and deletion. ? process suspension and resumption. ? Provision of mechanisms for: ? process synchronization ? process communication Operating Systems 1.57 Main-Memory Management ? Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices. ? Main memory is a volatile storage device. It loses its contents in the case of system failure. ? The operating system is responsible for the following activities in connections with memory management: ? Keep track of which parts of memory are currently being used and by whom. ? Decide which processes to load when memory space becomes available. ? Allocate and deallocate memory space as needed. Operating Systems 1.58 29 File Management ? A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. ? The operating system is responsible for the following activities in connections with file management: ? File creation and deletion. ? Directory creation and deletion. ? Support of primitives for manipulating files and directories. ? Mapping files onto secondary storage. ? File backup on stable (nonvolatile) storage media. Operating Systems 1.59 I/O System Management ? The I/O system consists of: ? A buffer-caching system ? A general device-driver interface ? Drivers for specific hardware devices Operating Systems 1.60 30 Secondary-Storage Management ? Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory. ? Most modern computer systems use disks as the principle on-line storage medium, for both programs and data. ? The operating system is responsible for the following activities in connection with disk management: ? Free space management ? Storage allocation ? Disk scheduling Operating Systems 1.61 Networking (Distributed Systems) ? A distributed system is a collection processors that do not ? ? ? ? share memory or a clock. Each processor has its own local memory. The processors in the system are connected through a communication network. Communication takes place using a protocol. A distributed system provides user access to various system resources. Access to a shared resource allows: ? Computation speed-up ? Increased data availability ? Enhanced reliability Operating Systems 1.62 31 Protection System ? Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources. ? The protection mechanism must: ? distinguish between authorized and unauthorized usage. ? specify the controls to be imposed. ? provide a means of enforcement. Operating Systems 1.63 Command-Interpreter System ? Many commands are given to the operating system by control statements which deal with: ? process creation and management ? I/O handling ? secondary-storage management ? main-memory management ? file-system access ? protection ? networking Operating Systems 1.64 32 Command-Interpreter System (Cont.) ? The program that reads and interprets control statements is called variously: ? command-line interpreter ? shell (in UNIX) Its function is to get and execute the next command statement. Operating Systems 1.65 Operating System Services ? Program execution – system capability to load a program into memory and to run it. ? I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. ? File-system manipulation – program capability to read, write, create, and delete files. ? Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing. ? Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs. Operating Systems 1.66 33 Additional Operating System Functions Additional functions exist not for helping the user, but rather for ensuring efficient system operations. • Resource allocation – allocating resources to multiple users • • Operating Systems or multiple jobs running at the same time. Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics. Protection – ensuring that all access to system resources is controlled. 1.67 System Calls ? System calls provide the interface between a running program and the operating system. ? Generally available as assembly-language instructions. ? Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++) ? Three general methods are used to pass parameters between a running program and the operating system. ? Pass parameters in registers. ? Store the parameters in a table in memory, and the table address is passed as a parameter in a register. ? Push (store) the parameters onto the stack by the program, and pop off the stack by operating system. Operating Systems 1.68 34 Passing of Parameters As A Table Operating Systems 1.69 Types of System Calls ? Process control ? File management ? Device management ? Information maintenance ? Communications Operating Systems 1.70 35 MS-DOS Execution At System Start-up Operating Systems Running a Program 1.71 UNIX Running Multiple Programs Operating Systems 1.72 36 Communication Models ? Communication may take place using either message passing or shared memory. Msg Passing Shared Memory Operating Systems 1.73 System Programs ? System programs provide a convenient environment for program development and execution. The can be divided into: ? File manipulation ? Status information ? File modification ? Programming language support ? Program loading and execution ? Communications ? Application programs ? Most users’view of the operation system is defined by system programs, not the actual system calls. Operating Systems 1.74 37 MS-DOS System Structure ? 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 Operating Systems 1.75 MS-DOS Layer Structure Operating Systems 1.76 38 UNIX System Structure ? 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. Operating Systems 1.77 UNIX System Structure Operating Systems 1.78 39 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. Operating Systems 1.79 An Operating System Layer Operating Systems 1.80 40 OS/2 Layer Structure Operating Systems 1.81 Microkernel System Structure ? Moves as much from the kernel into “user” space. ? 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 Operating Systems 1.82 41 Windows NT Client-Server Structure Operating Systems 1.83 Virtual Machines ? A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware. ? A virtual machine provides an interface identical to the underlying bare hardware. ? The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory. Operating Systems 1.84 42 Virtual Machines (Cont.) ? The resources of the physical computer are shared to create the virtual machines. ? CPU scheduling can create the appearance that users have their own processor. ? Spooling and a file system can provide virtual card readers and virtual line printers. ? A normal user time-sharing terminal serves as the virtual machine operator’s console. Operating Systems 1.85 System Models Non-virtual Machine Operating Systems Virtual Machine 1.86 43 Advantages/Disadvantages of Virtual Machines ? The virtual-machine concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines. This isolation, however, permits no direct sharing of resources. ? A virtual-machine system is a perfect vehicle for operating-systems research and development. System development is done on the virtual machine, instead of on a physical machine and so does not disrupt normal system operation. ? The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate to the underlying machine. Operating Systems 1.87 Java Virtual Machine ? Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM). ? JVM consists of - class loader - class verifier - runtime interpreter ? Just-In-Time (JIT) compilers increase performance Operating Systems 1.88 44 Java Virtual Machine Operating Systems 1.89 System Implementation ? Traditionally written in assembly language, operating systems can now be written in higher-level languages. ? Code written in a high-level language: ? can be written faster. ? is more compact. ? is easier to understand and debug. ? An operating system is far easier to port (move to some other hardware) if it is written in a high-level language. Operating Systems 1.90 45