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 & ManagementInterrupt & Exception HandlingProcess & Task ManagementProcess Scheduling &

SynchronizationFile SystemTiming

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.)

Scheduling

algorithm

CPU Overhead Throughput Turnaround

time

Response time

First In First Out Low Low High Low

Shortest remaining time

Medium High Medium Medium

Fixed priority pre-emptive scheduling

Medium Low High High

Round-robin scheduling

High Medium Medium High

Multilevel queue scheduling

High High Medium Medium