operating systems classification university
- 1. John Jose Associate Professor Department of Computer Science & Engineering Indian Institute of Technology Guwahati Lecture 1 Operating Systems – Classifications and Service CS343 Operating Systems
- 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 on hardware ❖ Make the computer system convenient to use ❖ Use the computer hardware in an efficient manner
- 3. Types of Operating Systems ❖ Most systems use a single general-purpose/special purpose processor ❖ There are several architectures which all require a different OS: ❖ Multiprogramming Systems ❖ Desktop PCs ❖ Parallel Systems ❖ Clustered Systems ❖ Real-time Systems ❖ Embedded Systems
- 4. ❖ 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), OS switches to another job Multiprogramming Systems
- 5. ❖ 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 ❖ Multiple programs executing in memory ❖ If several jobs ready to run at the same time CPU scheduling Timesharing Systems
- 6. Memory Layout for Multiprogrammed System
- 7. Desktop PCs ❖ Personal Computers – computer system dedicated to a single user. ❖ I/O devices – keyboards, mice, display screens, small printers. ❖ User convenience and responsiveness. ❖ Mostly single user - do not need advanced CPU utilization or protection features. ❖ May run several different types of operating systems (Windows, MacOS, UNIX, Linux)
- 8. Parallel Systems ❖ Multiprocessor systems with more than one CPU in close communication. ❖ Tightly coupled system – processors share memory and the internal clock; communication usually takes place through the shared memory. ❖ Loosely coupled system – multiple processors/computers with its own memory connected together for efficiency and throughput.
- 9. Multiprocessor/Parallel Systems ❖ Multiprocessors systems growing in use and importance ❖ Increased throughput ❖ Economy of scale ❖ Increased reliability – graceful degradation or fault tolerance ❖ Asymmetric Multiprocessing ❖ Symmetric Multiprocessing
- 10. Multiprocessor Systems ❖ Asymmetric Multiprocessing ❖ Each processor is assigned a specific task; master processor schedules and farms work to slave processors. ❖ More common in extremely large systems like mainframes with hundreds of processors.
- 11. Multiprocessor Systems ❖ Symmetric Multiprocessing ❖ Each processor runs an identical copy of the operating system. ❖ The OS code is usually shared. ❖ Many processes can run at once without performance deterioration. ❖ Most modern operating systems have SMP support. ❖ OS has to cater for protection of data.
- 12. Clustered Systems ❖ Like multiprocessor 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
- 13. Clustered Systems ❖ 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
- 14. ❖ 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 have either hard or soft real-time. Real-Time Systems
- 15. ❖ Personal Digital Assistants (PDAs) ❖ Smart telephones ❖ Issues: ❖ Limited memory, Slow processors, Small display screens. ❖ Emphasis is on I/O operations. ❖ Limited memory management and protection Embedded Systems
- 16. ❖ 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 Operating System in Dual Mode
- 17. Operating System in Dual Mode
- 19. Operating System Services ❖ The OS structure is divided into many sub-components. ❖ Process Execution ❖ Process Management ❖ Memory Management ❖ File Management ❖ Storage Management ❖ I/O Sub-system Management ❖ Protection and Security ❖ User Interface
- 20. Process Execution ❖ 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. ❖ OS must be able to load a program into memory, run that program, and end execution ❖ Assign resources like CPU, memory, I/O, files, data to accomplish its task ❖ Process termination requires reclaim of any reusable resources
- 21. 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
- 22. 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 ❖ Keeping track of which parts of memory are currently being used and by whom ❖ Deciding which processes and data to move into and out of memory ❖ Allocating and deallocating memory space as needed
- 23. File Management ❖ OS provides uniform, logical view of information storage ❖ Abstracts physical properties of storage to logical storage unit - file ❖ Files are usually organized into directories ❖ OS determines access control on files/directories that determine who can access what ❖ File-System management 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
- 24. Storage Management ❖ Mass storage devices (disks/ tape drives) store data that does not fit in main memory or data that must be kept for a long period of time ❖ Devices vary in access speed, capacity, data-transfer rate, access method ❖ OS activities in disk management includes ❖ Free-space management ❖ Storage allocation ❖ Disk scheduling
- 25. I/O Subsystem Management ❖ OS hides peculiarities of hardware devices from the user ❖ I/O subsystem responsible for ❖ 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) ❖ Providing device-driver interface
- 26. 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 ❖ Distinguish among users, to determine who can do what ❖ User identities (user IDs) and associated access controls on resources ❖ Group identifier (group ID) associated access controls on resources ❖ Privilege escalation to change to give more rights
- 27. User Interface ❖ Provides a user-friendly platform to initiate actions from user side. ❖ The UI primarily receives command from user and executes it ❖ Command-Line Interface (CLI) allows direct command entry ❖ User-friendly desktop Graphical User Interface (GUI) ❖ Usually mouse, keyboard, and monitor used for giving inputs. ❖ Icons represent files, programs, actions, etc ❖ Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory) ❖ Many systems (Microsoft, Apple-Mac OS, UNIX) now include both CLI and GUI interfaces