Operating System PowerPoint Presentation

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Operating System

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Over View Of Operating System An operating system acts as an intermediary between the user of a computer and the computer hardware An operating system is software that manages the computer hardware.

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Introduction An operating system is a program that manages a computer’s hardware. It also provides a basis for application programs It acts as an intermediary between the computer user and the computer hardware

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What is an operating system?  An operating system is the program that initially loaded into the computer by a boot program Manages all the other programs in a computer The other programs are called applications or application programs Users can interact directly through a user interface

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Operating System A Program or set of Programs or even some part of hardware that provides mainly three functionalities User Interface to communicate with Machine and other resources connected. Provide resource management for efficient and error free resource usage Provide security and protection

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Abstract View

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Operating System

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Operating System

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Common Examples Mobile operating system (OS) specifically designed to run on mobile devices NOS(network operating system) includes special functions for connecting Computers

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kernel The core of operating system The operating system is the one program running at all times on the computer usually called the kernel. Along with the kernel, there are two other types of programs: system programs, application programs

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Operating System Design and Implementation Start by defining goals and specifications Affected by choice of usage, type of system & hardware, User goals System goals Internal structure of different Operating Systems varies widely

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User View and System View The user’s view of the computer varies according to the interface being used. The goal is to maximize the work From the computer’s point of view, the operating system is the program most intimately involved with the hardware. In this context, we can view an operating system as a resource allocator.

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Computer-System Operation when it is powered up or rebooted it needs to have an initial program to run. This initial program, or bootstrap program, tends to be simple.

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Boot To load the first piece of software that starts a computer. Boot is short for bootstrap, Short for bootstrap, the starting-up of a computer, which involves loading the operating system and other basic software. Cold boot Warm boot

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Operating System Design and Implementation Important principle is to separate Policy: What will be done? Mechanism: How it will be done? The separation of policy from mechanism is a very important, that: Allows maximum flexibility in policy decisions Compromises the policy least The Mechanism: if it is to be done it is done, however, for efficiency, convenience and other parameters, may need Policy to be changed later

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Killer application  Any computer program that is so necessary or desirable  it proves the core value of some larger technology substantially increase sales of the platform on which it runs  first examples of a killer application the VisiCalc  for the Apple II series

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CPU modes Unrestricted mode kernel mode Restricted modes user modes Multiple user modes often with a hierarchy of privileges often called protection rings

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Transition from user to kernel mode

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CPU modes Applications run in user mode Core operating system components run in kernel mode Many drivers run in kernel mode but some drivers run in user mode Windows creates a process for user mode applications

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Kernel mode Vs User modes

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Protection ring

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Protection ring Hierarchical protection domains Often called protection rings Protect data and functionality from faults and malicious behavior

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System Structure Monolithic Approach (Most of OS activities in single module) Non modular, non maintainable, usually in-efficient Hierarchical design, View the system as a series of levels Layers converge from logical to physical activities Each level performs a subset of functions Each level relies on the next lower level to perform more primitive functions Each layer has well defined interface for communication This decomposes a problem into a number of more manageable sub-problems

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Simple Structure MS-DOS – written to provide the most of functionality in the least space to a single user Not divided into modules, neither strictly monolithic. Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated BIOS is provided by vendor to accommodate design variations in hardware.

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MS-DOS Layer Structure

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Layered Approach The operating system is divided into a number of layers (levels), each built on top of lower layers. With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers From higher to lower layer, the functionality moves from logical level to physical.

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Layered Operating System

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Operating System Design Hierarchy Level Name Objects Example Operations 13 Shell User programming Shell scripts, statements in shell environment language 12 User processes User processes Quit, kill, suspend, resume 11 Directories Directories Create, destroy, attach, detach, search, list 10 Devices External devices, such Open, close, as printer, displays read, write and keyboards 9 File system Files Create, destroy, open, close read, write Communications Pipes Create, destroy, open. close, 7 Virtual Memory Segments, pages Read, write, fetch 6 Local secondary Blocks of data, device Read, write, allocate, free store channels read, write

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Operating System Design Hierarchy (cont) Level Name Objects Example Operations 5 Primitive processes Primitive process, Suspend, resume, wait, signal semaphores, ready 4 Interrupts Interrupt-handling Invoke, mask, unmask, retry programs, Procedures Procedures, call stack, Mark stack, call, return 2 Instruction Set Evaluation stack, micro- Load, store, add, subtract program interpreter, branch scalar and array data 1 Electronic circuits Registers, gates, buses, Clear, transfer, activate, etc. (Hardware) complement

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Object oriented Systems Object-oriented design used for adding modular extensions to a small kernel Enables system programmers to customize an operating system Additions / modifications can be made without disrupting the existing system integrity Reusability Easy to maintain

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Thread A thread is a basic unit of CPU utilization, consisting of a program counter, a stack, and a set of registers, ( and a thread ID. ) Traditional ( heavyweight ) processes have a single thread of control There is one program counter, and one sequence of instructions that can be carried out at any given time

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How threads differ from processes Processes are typically independent, while threads exist as subsets of a process Processes carry considerably more state information than threads, whereas multiple threads within a process share process state as well as memory and other resources Processes have separate address spaces, whereas threads share their address space Processes interact only through system-provided inter-process communication mechanisms Context switching between threads in the same process is typically faster than context switching between processes.

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What is paging? Why paging is used? Paging is a memory management technique in which the memory is divided into fixed size pages Paging is used for faster access to data When a program needs a page, it is available in the main memory as the OS copies a certain number of pages from your storage device to main memory. Paging allows the physical address space of a process to be noncontiguous.

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Storage Structure General-purpose computers run most of their programs from rewritable memory, called main memory (also called random-access memory, or RAM).

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Storage-device hierarchy

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Operating System Concepts (1): Process Management A process tree A created two child processes, B and C B created three child processes, D, E, and F

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Operating System Concepts (2): Deadlock Handling (a) A potential deadlock. (b) an actual deadlock.

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Metric Units The metric prefixes

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Interrupt The occurrence of an event is usually signaled by an interrupt from either the hardware or the software. Hardware may trigger an interrupt at any time by sending a signal to the CPU Software may trigger an interrupt by executing a special operation called a system call

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Interrupt  A signal to the operating system that an event has occurred hardware interrupt software interrupt Trap mode switch  context switch

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Polling Polling, or polled operation Refers to actively sampling the status of an external device by a client program Polling is most often used in terms of input/output (I/O), and is also referred to

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Operating system virtualization Operating system virtualization refers to the use of software To allow system hardware to run multiple instances of different operating systems concurrently allowing you to run different applications requiring different operating systems on one computer system The operating systems do not interfere with each other or the various applications

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Classification of Operating systems Multi-user Multiprocessing Multitasking Multithreading Real time

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User interface Abbreviated UI, the junction between a user and a computer program. An interface is a set of commands or menus through which a user communicates with a program. A driven interface is one in which you enter commands. A driven interface is one in which you select command choices from various menus displayed on the screen. The user interface is one of the most important parts of any program because it determines how easily you can make the program do what you want.

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Multi-user Refers to computer systems that support two or more simultaneous users. Some operating systems permit hundreds or even thousands of concurrent users. All mainframes and minicomputers are multi-user systems, but most personal computers and workstations are not. Another term for multi-user is time sharing.

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Single-user interface An operating system that is usable by only one user at a time. An application that provides single interface from which a user can access multiple applications.

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Multi-user interface Multi-user interface typically refers to an operating system that allows concurrent access by multiple users on the system. Multiprocessing : Supports running a program on more than one CPU. Multitasking : Allows more than one program to run concurrently. Multithreading : Allows different parts of a single program to run concurrently. Real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

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Multiprocessing Refers to a computer system's ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently. UNIX is one of the most widely used multiprocessing systems, but there are many others, including OS/2 for high-end PCs. Multiprocessing systems are much more complicated than single-process systems because the operating system must allocate resources to competing processes in a reasonable manner. Refers to the utilization of multiple CPUs in a single computer system. This is also called parallel processing.

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Symmetric multiprocessing architecture

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A dual-core design with two cores placed on the same chip

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Multithreading The ability of an operating system to execute different parts of a program, called threads, simultaneously The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other

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RDI - Remote Debug Interface RDI is short for Remote Debug Interface The Remote Debug Interface (RDI) is an Application Programming Interface (API) that defines a standard set of data structures and functions that abstract hardware for debugging purposes. The Remote Debug Interface has for ten years served as a useful and widely adopted interface between debuggers and debug target (simulators, emulators and monitors) for the ARM architecture.

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Spooling Acronym for simultaneous peripheral operations on-line, spooling refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready  Spooling is useful because devices access data at different rates.

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Real time Occurring immediately The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input immediately They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption.

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Multitasking The ability to execute more than one task at the same time, a task being a program. The terms multitasking and multiprocessing are often used interchangeably, In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time. There are two basic types of multitasking: preemptive and cooperative.

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Cooperative multitasking A type of multitasking in which the process currently controlling the CPU must offer control to other processes. It is called cooperative because all programs must cooperate for it to work. If one program does not cooperate, it can hog the CPU. In contrast, preemptive multitasking forces applications to share the CPU whether they want to or not

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Multithreading vs Multitasking Multitasking is referred to as a feature of OS Multithreading is the feature of process Multitasking means an OS can have multiple processes(tasks) run simultaneously, Multithreading means in any single process, multiple threads is allowed and again, Multitasking is sharing of computing resources(CPU, memory, devices, etc.) among processes, while multithreading is sharing of computing resources among threads of a single process

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Caching Caching is an important principle of computer systems. Information is normally kept in some storage system As it is used, it is copied into a faster storage system the cache on a temporary basis

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Performance of various levels of storage

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Migration of integer A from disk to register