1. 1 CIS450/IMSE450/ECE478 Operating Systems Winter 2003 Professor Jinhua Guo

2. 2 Expectations This class IS about … –Principles of modern OS’s management of processes, memory, files, and I/O devices –Implementation of several OS features This class IS NOT about … –How to use particular OS’s Ex. How do I install the Linux on my PC?

3. 3 What is an Operating System? It is just a program Performs two functions –Make computer system convenient to use Example: don’t worry about CPU scheduling –Manage machine’s resources efficiently Example: many users want printer Convenience and Efficiency conflict

4. 4 Computer System Components

5. 5 Computer Systems Mainframe Systems Desktop Systems Parallel Systems (Multiprocessor Systems) Distributed Systems Clustered Systems Real-Time Systems Handheld Systems

6. 6 Mainframe Systems User as Console Operator Batch Systems Multiprogramming Systems Time-Sharing Systems

7. 7 Batch Systems Group similar jobs together –Improved throughput Eventually developed simple monitor –The computer no longer had to wait for human operator –Reduced CPU idle time

8. 8 Multiprogramming Systems What to do when I/O going on? –Let another user run Multiple processes active at once –Benefit: small jobs not delayed by large ones Process A waiting for disk => process B runs Getting closer to modern OS: –Require scheduling, multiple processes in memory, protection, etc.

9. 9 Timesharing Systems - Interactive Each user has own terminal. Strive for good response time The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). A job swapped in and out of memory to the disk. Ex: early UNIX systems

10. 10 Desktop Systems With VLSI, price of computer has dropped Back to single user computers –why need timesharing – only one user! –why need protection – only one user! Users want to be able to run multiple processes –Listening music while working Need protection –www Ex: DOS, Windows, MacOS, UNIX, Linux

11. 11 Parallel Systems Multiprocessor systems with more than on CPU in close communication. Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. Advantages of parallel system: –Increased throughput –Economical –Increased reliability graceful degradation Fault tolerance

12. 12 Distributed Systems Distribute the computation among several physical processors. Geographically dispersed hosts. Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines. Advantages of distributed systems. –Resources Sharing –Computation speed up – load sharing –Reliability –Communications

13. 13 Clustered Systems Clustering allows two or more systems to share storage. Provides high reliability. Asymmetric clustering: one server runs the application while other servers standby. Symmetric clustering: all N hosts are running the application.

14. 14 Real-Time Systems Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. Well-defined fixed-time constraints. Real-Time systems may be either hard or soft real-time.

15. 15 Handheld Systems Personal Digital Assistants (PDAs) Cellular telephones Issues: –Limited memory –Slow processors –Small display screens Ex: PalmOS, Windows CE

16. 16 Computing Environments Traditional computing Web-Based Computing Embedded Computing Pervasive Computing Mobile Computing Ubiquitous Computing