Group no.2 Presented to : Eng.Ahmed Hassan Sunday, March 04,2012

 Operating system (OS)  Examples of Operating system  RTOS  Soft versus Hard RTOS  Operating System Scheduling  Types of operating system scheduling  Scheduling algorithms Scope

 A program that controls the execution of application programs  An interface between applications and hardware Operating System

 Memory Addressing & Management  Interrupt & Exception Handling  Process & Task Management  Process Scheduling & Synchronization  File System  Timing Operating System handles

 RTOS – Real-Time Operating System  Single-user, Single-task: example PalmOS  Single-user, Multi-task: MS Windows and MacOS  Multi-user, Multi-task: UNIX Examples of Operating Systems

 A real-time operating system (RTOS)  It is an operating system (OS) intended to serve real-time application requests.  It is part of program (or source code) that was written for manage the CPU usability of microcontroller and it help to improve the efficiency of CPU in managing the tasks or process. What is RTOS

 valued more for how quickly it can respond than for the amount of work it can perform in a given period of time.  Real-time operating systems themselves have two varieties, soft real-time systems and hard real-time systems. What is RTOS (cont.)

 In a soft real-time system, tasks are completed as fast as possible without having to be completed within a specified timeframe.  In a hard real-time operating system however, not only tasks must be completed within the specified timeframe, but they must also be completed correctly. Soft vs. Hard RTOS

 Scheduling is the method by which threads, processes or data flows are given access to system resources. Operating System Scheduling

 The need for a scheduling algorithm arises from the requirement for most modern systems to perform  multitasking (execute more than one process at a time) and,  multiplexing (transmit multiple flows simultaneously). Operating System Scheduling(cont.)

 Throughput:- number of processes that complete their execution per time unit.  Waiting Time:- equal CPU time to each process.  Turnaround:- total time between submission of a process and its completion.  Response Time:- amount of time it takes from when a request was submitted. The scheduler is concerned with

How Scheduling manage task execution  A task, also referred to as a thread, is an independent section of a program complete with its own stack and CPU register space.  Each task is assigned a priority, and is always placed in one of dormant, ready, running, waiting.

 A task is ready when it is available for execution but its priority is less than the current task priority of the system.  Consequently, a task is running when its current priority is met and the CPU starts to execute it.  A task is considered in wait mode when it is waiting for a resource to become available How Scheduling manage tasks execution (cont.)

 Long-term scheduling  Medium-term scheduling  Short-term scheduling Types of OS scheduling

 These are algorithms used for distributing resources among parties which simultaneously and asynchronously request them. Scheduling Algorithms

 First in first out also known “First Come First served ( FCFS ) “  Shortest remaining time or (SJF)  Fixed priority pre-emptive scheduling  Round-robin scheduling  Multilevel queue scheduling Scheduling Algorithms(cont.)