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Operating Systems

Learn about the importance of operating systems in managing hardware and software resources, providing a consistent application interface, and ensuring efficient processor, memory, device, and storage management.

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Operating Systems

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  1. Operating Systems

  2. Operating systems • Most important program that runs on a computer • Every general-purpose (such as desktop) computer must have OS to run other programs • Manages the hardware and software resources of the system • Provides stable and consistent way for applications to deal with the hardware without having to know all the details • Most common • Windows, UNIX, Macintosh • Many other OS designed for special-purpose applications • mainframes, robotics, manufacturing, real-time control systems

  3. Starting the computer • BIOS loads the bootstrap loader (or bootstrap program) from a known location on disk and starts it • Bootstrap loader looks for the OS kernel and loads it into memory • The kernel initializes the hardware present in the system and loads required drivers • OS begins loading services and application programs and shows the user interface

  4. Managing hardware and software • Various programs and input methods compete for the attention of the central processing unit (CPU) • programs and methods demand memory, storage and input/output (I/O) bandwidth for their own purposes • OS makes sure each application gets the necessary resources while cooperating with the other applications • economizes capacity of the system to greatest benefit of users and applications.

  5. Software  OS  Hardware

  6. Providing consistent application interface • Important if more than one type of computer is using OS or if computer hardware is open to change • A consistent application program interface (API) allows software developer to write an application on one computer and have a high level of confidence that it will run on another computer of the same type • even if the amount of memory or the quantity of storage is different on the two machines • OS can ensure that applications continue to run when hardware upgrades and updates occur • OS and not the application is charged with managing the hardware and the distribution of its resources

  7. Tasks of the OS • A task refers to the combination of a program being executed and bookkeeping information used by the operating system • Tasks of the OS: • Processor management • Memory management • Device management • Storage management • Application interface • User interface

  8. Processor management • Ensuring that each process and application receives enough of the processor's time to function properly • Using as many processor cycles for real work as is possible • Processes (thread) • schedule work done by processor • CPU can only do one thing at a time • OS has to switch between different processes thousands of times a second • OS sets a certain number of CPU execution cycles to one program, after those cycles switches to another program, etc.

  9. Memory and storage management • Each process must have enough memory in which to execute, and it can neither run into the memory space of another process nor be run into by another process • The different types of memory in the system must be used properly so that each process can run most effectively • Memory types • High-speed cache - fast, small amounts of memory available to the CPU, where cache controllers predict which data CPU will need next and pull it from main memory • Main memory - RAM • Secondary memory - disk

  10. Virtual memory • The memory installed in a computer is called physical memory • limited in size and shared by all processes • Virtual memory assigns a different address space to every process • address 5 for process 1 describes a different location in physical memory than address 5 for process 2 • prevents processes from accessing each others memory (memory protection) • OS can allocate more space in virtual memory than is present in physical memory by using paging

  11. Paging • OS must balance the needs of the various processes with the availability of the different types of memory • Not enough memory to run all processes simultaneously • Processes not running take up space in memory • Paging: allocating physical memory to processes in fixed-size blocks called pages • Separate programs into pages and keep only a few pages of each running program in memory at one time • active pages kept in memory • inactive pages kept on disk, brought in as needed • Moving pages in and out of memory is called swapping

  12. Thrashing • If user runs too many processes at the same time, OS will use majority of its available CPU cycles to swap between processes rather than run processes • Paging or swapping systems that are overloaded waste most of their time moving data rather than performing useful computation Thrashing • CPU utilization, system throughput and system response time decrease resulting poor performance of a system • Risk of thrashing increases with degree of multi-programming

  13. Device management • Device driver • path between the operating system and (most) hardware not on computer's motherboard • translator between signals of the hardware subsystems and high-level programming languages of the OS and application programs • takes file data from OS and translates into bit streams put in specific locations on storage devices • Drivers are run when device is required, function basically like any other process • OS assigns high-priority blocks to drivers so hardware resources can be released and readied for further use as quickly as possible

  14. Application and user interfaces • Application Program Interfaces (APIs) • allow application programmers to use functions of computer and OS without worrying about details of CPU operation • provides a consistent way for applications to use the resources of the computer system • User Interface (UI) • brings structure to the interaction between a user and the computer • program or set of programs that sits as a layer above the OS • usually a graphical user interface (GUI)

  15. Classification • Multi-user • allows many different users to take advantage of the computer's resources simultaneously • Single-user, multi-tasking • single user operates many programs at same time • most desktop and laptop computers today • Single-user, single task • one user can do one thing at a time (e.g. Palm OS) • Real time (RTOS) • particular operation executes in precisely the same amount of time every time it occurs • machinery, scientific instruments and industrial systems

  16. Types of operating systems

  17. Open Source • Description of software distributed as source code under licenses that guarantee everyone the right to freely use, change, or redistribute the source code • Initiated by Bruce Perens • primary author of The Open Source Definition, the formative document of Open Source movement The basic idea behind open source is very simple: Whenprogrammers can read, redistribute, and modify the sourcecode for a piece of software, the software evolves. Peopleimprove it, people adapt it, people fix bugs. And this canhappen at a speed that, if one is used to the slow pace ofconventional software development, seems astonishing. www.opensource.org

  18. Open Source definition • Distribution terms of open-source software must comply with the following criteria: • free redistribution • source code • derived works • integrity of the author's source code • no discrimination against persons or groups • no discrimination against fields of endeavor • distribution of license • license must not be specific to a product • the license must not restrict other software • the license must be technology-neutral www.opensource.org

  19. The GNU Project • Founded by Richard Stallman • Launched in 1984 to develop a complete free Unix- like operating system: GNU • GNU Manifesto • written by Stallman at start of GNU Project to ask for participation and support • GNU is free software • everyone is free to copy and redistribute it as well as make changes either large or small • www.gnu.org

  20. Linux • Linux is a Unix-like kernel, created by Linus Torvalds in 1991 • Linux together with the GNU operating system made a complete free system: a Linux-based version of the GNU system • GNU/Linux system • GNU/Linux systemsare in widespread use • estimated 20 million users • Complete, free OS

  21. References • www.webopedia.com • www.howstuffworks.com • www.linux.org • www.microsoft.com • www.apple.com • www.opensource.org • www.stallman.org • www.gnu.org • www.perens.com • FOLDOC

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