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Course: Operating Systems Instructor: M Umair 1 M Umair – http://www.m-umair.com Introduction 2 M Umair – http://www.m-umair.com About the course Instructor’s Introduction Course outline – Reference Books What to expect Lectures – Supporting Material Quizzes & Assignments Course Website Questions ? 3 M Umair – http://www.m-umair.com Prelude 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. The operating system is the one program running at all times on the computer—usually called the kernel. Can you name some of the popular operating systems ? { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 4 Prelude { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 5 Prelude { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 6 Simple Batch Systems Hire an operator Add a card reader 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 back to monitor { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 7 Simple Batch Systems Operating System User Program Disk Card Reader CPU Line Printer Spooling Memory Layout { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 8 Multi Programmed Batch Systems Operating System Jobs stored in Job pool ready to be brought into memory Job Scheduling Job 1 Job 2 Having many programs in memory Memory Management Job 3 Several jobs ready for execution CPU Scheduling Job 4 Many other considerations as well Memory Layout { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 9 Time Sharing Systems 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 is swapped in and out of memory to the disk. A time sharing OS allows many users to share the computer simultaneously. Switching is done rapidly. List the complexities of time sharing system ? { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 10 Parallel Systems Multiprocessor systems with more than one 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 { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 11 Parallel Systems Symmetric multiprocessing (SMP) Each processor runs an identical copy of the operating system. Most modern operating systems support SMP Asymmetric multiprocessing Each processor is assigned a specific task; master processor schedules and allocates work to slave processors. More common in extremely large systems { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 12 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. Hard real-time system Soft real-time system { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 13 Real Time Systems Hard real-time system. Secondary storage limited or absent, data stored in short-term memory, or read-only memory (ROM) Conflicts with time-sharing systems, not supported by generalpurpose operating systems. Soft real-time system Limited utility in industrial control or robotics Useful in applications (multimedia, virtual reality) requiring advanced operating-system features. { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 14 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 high-speed buses or telephone lines. Advantages of distributed systems. Resources Sharing Computation speed up – load sharing Reliability Communications { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 15 Distributed Systems Network Operating System Provides file sharing Provides communication scheme Runs independently from other computers on the network Distributed Operating System Less autonomy between computers Gives the impression there is a single operating system controlling the network. { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 16 Interrupts Modern operating systems are interrupt driven. Events are signaled by the occurrence of an interrupt or a trap. A trap (or an exception) is a software-generated interrupt. IVT (interrupt vector table) Any example of trap? { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 17 DMA 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. { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 18 Dual-Mode Operation How to distinguish between the execution of operating-system code and user defined code? Two separate modes of operation: user mode and kernel mode (also called supervisor mode, system mode, or monitor mode). A bit, called the mode bit, is added to the hardware of the computer to indicate the current mode: kernel (0) AND user (1). { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 19 Dual-Mode Operation The machine instructions that may cause harm are known as privileged instructions. All I/O instructions are privileged instructions. The hardware allows privileged instructions to be executed only in kernel mode. { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 20 Dual-Mode Operation - Example { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 21 Dual-Mode Operation - Example { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 22 Dual-Mode Operation - Example { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 23 Dual-Mode Operation - Case The lack of a hardware-supported dual mode can cause serious shortcomings in an operating system. For instance, MS-DOS was written for the Intel 8088 architecture, which has no mode bit and therefore no dual mode. A user program can wipe out the operating system by writing over it with data. Multiple programs are able to write to a device at the same time, with potentially disastrous results. { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 24 Weekly Tasks Describe the differences between symmetric and asymmetric multiprocessing. What are three advantages and one disadvantage of multiprocessor systems? What is the purpose of interrupts? What are the differences between a trap and an interrupt? Can traps be generated intentionally by a user program? If so, for what purpose? Read about Memory & CPU protection? { Ref: Operating System Concepts 8th Edition | Abraham Silberschatz , Greg Gagne , Peter B. Galvin } M Umair – http://www.m-umair.com 25