Lecture Operating System University New.
- 1. Dr. Maria Kanwal Assistant Professor Dept. of Computer Sciences, MY University 1
- 2. About Today’s Lecture Summary Single-user systems Batch systems Multi programmed systems Time-sharing systems Real time systems Reading Material Operating Systems Concepts, Chapter 1 PowerPoint Slides 2
- 3. Single-user systems A computer system that allows only one user to use the computer at a given time is known as a single-user system. The goals of such systems are maximizing user convenience and responsiveness, instead of maximizing the utilization of the CPU and peripheral devices. Single-user systems use I/O devices such as keyboards, mice, display screens, scanners, and small printers. They may run different types of operating systems, including DOS, Windows, and MacOS. Linux and UNIX operating systems can also be run in single-user mode. 3
- 4. Batch Systems Early computers were large machines run from a console with card readers and tape drives as input devices and line printers, tape drives, and card punches as output devices. The user did not interact directly with the system; instead the user prepared a job, (which consisted of the program, data, and some control information about the nature of the job in the form of control cards) and submitted this to the computer operator. The job was in the form of punch cards, and at some later time the output was generated by the system— user didn’t get to interact with his/her job. 4 Operating System Concepts (CSC-203). Week 1, Lecture 1
- 5. Multi-programmed Systems Multi-programming increases CPU utilization by organizing jobs so that the CPU always has one to execute. The operating system keeps several jobs in memory simultaneously. This set of jobs is a subset of the jobs on the disk which are ready to run but cannot be loaded into memory due to lack of space. Since the number of jobs that can be kept simultaneously in memory is usually much smaller than the number of jobs that can be in the job pool; the operating system picks and executes one of the jobs in the memory. 5
- 6. Multi-programmed Systems ... Cont’d Eventually the job has to wait for some task such as an I/O operation to complete. In a non multi-programmed system, the CPU would sit idle. In a multi-programmed system, the operating system simply switches to, and executes another job. When that job needs to wait, the CPU simply switches to another job and so on. 6
- 7. Time-sharing systems A time-sharing system is multi-user, multi-process, and interactive system. This means that it allows multiple users to use the computer simultaneously. A user can run one or more processes at the same time and interact with his/her processes. A time-shared system uses multiprogramming and CPU scheduling to provide each user with a small portion of a time-shared computer. Each user has at least one separate program in memory. To obtain a reasonable response time, jobs may have to be swapped in and out of main memory. UNIX, Linux, Widows NT server, and Windows 2000 server are timesharing systems 7
- 8. Real time systems Real time systems are used when rigid time requirements are placed on the operation of a processor or the flow of data; thus it is often used as a control device in a dedicated application. Examples are systems that control scientific experiments, medical imaging systems, industrial control systems and certain display systems. A real time system has well defined, fixed time constraints, and if the system does not produce output for an input within the time constraints, the system will fail. For instance, it would not do for a robot arm to be instructed to halt after it had smashed into the car it was building. 8
- 9. Handheld Systems Personal Digital Assistants (PDAs) Cellular telephones Issues: Limited memory Slow processors Small display screens 9
- 10. End of Today’s Lecture 10 Operating System Concepts (CSC-203). Week 1, Lecture 1