 Hello myself, Ravindra Chauhan, Assistant Professor, Department of Electronics Engineering, Walshand Institute of Technology, Solapur. In this session, we will discuss the concepts of the operating system and also we will introduce the real-time operating system. Taking outcome from this session, at the end of this session, student will be able to compare RTOS and General Purpose Operating System and they are able to classify the RTOS. RTOS stands for Real-Time Operating System. The outline of the session, first we will see what the operating system is. The various functions of the operating system, classification of operating system and the special operating system called the RTOS and its various types. An operating system is a software that allows the user to use the hardware resources easily. Now, the hardware resources means the different input and output devices like the keyboard, the printer and all other similar hardware devices. Operating system provides the interface between the user and the physical hardware, means an operating system always lies between the user and the hardware, means the user is accessing all the hardware through the software which is called the operating system. Any computing system or processor-based system, its hierarchical structure will look like this. At the bottom of the system, the hardware is lying, hardware means all the physical components and the devices, but only the hardware is of no use. So to drive this hardware, some sort of software is required and that software is called the operating system. So the operating system manages and controls the operation of all the physical hardware devices. So above the hardware, it is required to install the one of the operating system. Then above the operating system, one can install one or more required application programs like the MS Office or the software for hotel management and etc. And then above that, the user is actually accessing the hardware through the application program and the operating system. The major functions of operating system, the first one is called the resource management. Resource management function of an operating system allocates the computer resources such as CPU time, main memory, secondary storage space and input and output devices for the user. Data management functions is the operating system governs the input and output of data and their location, storage and retrieval. Also operating system is responsible for storing and retrieving the information on disk drives and for the organization of that information on the drive. Job management. Now here the meaning of job is nothing but it is a collection of one or more related programs and their associated data. The job management function of an operating system prepares, schedules, controls and monitors jobs submitted for execution to ensure the most efficient processing. Since for example, in job management function, the operating system allocates the CPU time for the different jobs. The operating system also establishes a standard means of communication between users and their computer systems. Operating system provides a user interface and standard set of commands that control the hardware. Means for example, the operating system provides the interface of the input device like the keyboard means user can access the system through the input device called the keyboard. The user interface allows the user to communicate with the operating system means user can communicate with the operating system through the input device for example, keyboard. Now the different types of operating systems are there. The first operating system is called the single user single tasking operating system. Means only one user work on this operating system and only one user performs the one task at a time. Example of single user single tasking operating system is MS-DOS and PAM operating system. Now these operating systems require very less amount of space on disk and that's why these operating systems runs on inexpensive computers means lowly configured systems. Another classification is done which is called single user multitasking operating system. Now this operating system can operate by a single user but that single user performs the number of tasks at the same time. This is the most common form of operating system nowadays. All of the single user multitasking operating system is Windows XP and OS X. This operating system requires expensive computers means highly configured computers it requires large amount of storage space and that's why this operating system is somewhat be a complex. Another type is called the multi user multitasking operating system. Means more number of users can perform more number of tasks at the same time. So many users connect to one computer and each user has a unique session. Example Unix, Linux and VMS. The maintenance of these operating systems can be easy but it requires a powerful computer means highly configured computers. The next operating system is called the real time operating system which is very fast but as far as the size of this operating system is concerned it is very small. That's why these operating systems can be built into a device along with the hardware. But the RTOS responds quickly to the user input. The application of the real time operating system it can be used in the device like the mp3 players, the some medical devices, the different phones etc. Now you pause the video and compare the general operating system and the real time operating system. General operating systems usually used for desktop and server applications it is the separate from application programs, no timing constraint on execution of applications, windows, linux etc. But the CPU utilization and throughput is important. Throughput means general OS must be capable to drive more number of input and output devices. Real time operating systems it is embedded in the hardware along with the applications. It is useful for systems with dedicated functionality, timing constraint on execution of applications, examples are E-Cos, VX-Works etc. Throughput is not important but the system can be timely. It may be inefficient but must be timely. The RTOS is typically an embedded operating system. The correctness of an action or function is decided not only by the logical results of the computation but also by the physical instance at which the results are produced. It is expected to fulfill the timing constraint required by various functionalities in the embedded system. The real time system must react to the input stimuli within deterministic time limit as dictated by the system requirements. Real time does not mean fast, real time means predictable. Example is DVD player. The video frames must be available at regular interval of 25ms. If multiple frames are clustered with long interframe gap the player cannot play it properly. Mainly the RTOS are classified as hard real time RTOS and soft real time RTOS. Example of hard real time used in jet airplane where the operations are very complex, hence it required the operating system. Most of the tasks are time critical so if deadline is violated the results can be catastrophic. Soft real time RTOS can be used in the iPhone which is the complex and hence required the operating system. Few tasks are time critical so if deadline is violated the results are not so catastrophic. References are Micro C book titled as the real time kernel by Gene Labros, real time operating system by Gene Cooling and embedded slash real time system by Dr. K. V. K. Prasad. Thank you.