The document discusses real-time operating systems (RTOS). It defines what an RTOS is and its key components: task management, memory management, intertask communication, and intertask synchronization. It also outlines the requirements of an RTOS, including being multi-tasking, preemptible, supporting task priorities and synchronization mechanisms, avoiding priority inversion, and being deterministic.

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7. Evolution of OS OS was evolved in the following way: 1) Serial processing 2) Batch processing 3) Multi-Programming Serial Processing RTOS Batch Processing Multi programming

9. Serial Programming Drawbacks 1) Low utilization of system resources. 2) User productivity is low. Program 1 Program 2 P1 IDLE P1 IDLE P2 IDLE P2 IDLE P1 P2

11. Multi - Programming Program1 Program2 P1 P2 P1 P2 P1 P2

12. Types of OS OS Size Function Multi-Programming Ex:Unix,WinNT Multi-Tasking Ex:RTX-51 Smaller Ex:RTX-51 Larger EX:WinNT,Unix

13. 1) Architecture For Larger OS CPU I/O Devices I/O Sub System File Manager Language Support Utilities Application Programs Kernel Scheduler Dispatcher Int.handler

14. 2) Architecture For Smaller OS CPU I/O Devices Application Programs Kernel Scheduler Dispatcher Int.handler

16. 3) Multi-Programming OS = Multi-Tasking + * Forms of memory protection * Enforces concurrency control when processes access shared I/O devices and files. 3) Multi-Programming OS

17. Real-Time Systems Systems in which correct responses are produced within a definite time limit. If computer responses exceed these time boundary then performance degradation and/or malfunction results. (or) Systems that are used in environments where a larger number of events, mostly external to computer system, must be accepted and processed in short time / within certain deadlines. (or) Any system in which time at which output is produced is significant.This is because input corresponds to some movement in physical world and output has to relate to that same movement.The lag from input time to output time must be small for acceptable timeliness.

19. Classification of Real-Time Systems Hard Real-Time Systems Soft

22. RTOS Real-time operating systems helps to build real-time system.

23. System tasks Application tasks Resource allocation Command Processor I subsystem File manager Task management Interrupt service routine Real time clock User level Operating system level Structure of a real time OS

25. Functions of RTOS – 1.Task Management Allocation of memory and CPU time to task. a) Scheduler: To keep a record of the state of each task To schedule the allocation of CPU time to each task. b) Dispatcher: To perform the context-switching.

26. Task State Diagram New Ready Running Halted Waiting

28. Scheduling Algorithms a) First-Come-First-Served (FCFS) b) Shortest Job First (SJF) c) Priority based Pre-emption d) Round-Robin (RR)

30. Various mechanism available are (a) Pipes (b) Message queues (c) Remote procedural calls (RPC) Functions of RTOS – 3.Intertask Communication

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