1. B.Ramamurthy9/19/20151 Operating Systems u Bina Ramamurthy CS421

2. B.Ramamurthy9/19/20152 Topics for discussion u What will you learn in this course? (goals) u What is an Operating System (OS)? u Evolution of OS u Important OS Components u Major achievements u Operating system design hierarchy u Sample systems

3. B.Ramamurthy9/19/20153 Goals for the course u Study the working of an OS. u Study the design and implementation of various components of an OS. u Learn about the alternatives available to a designer at all levels of abstraction in an OS. u Learn concurrent programming using processes, threads, and system calls. u Understand the basics of distributed systems. u Explore how you may contribute to solving many open problems in OS and distributed systems.

4. B.Ramamurthy9/19/20154 What is an Operating system? u Interface manager –Human interaction made easy –interfacing, abstraction, control and sharing u Resource manager –Efficient use of resources u Enhances hardware features –“virtual” time, space and resource (processes, threads) u System and data security and protection provider

5. B.Ramamurthy9/19/20155 User Interface u An end-user views the computer through an application. u Operating system provides these facilities for the user: –Program creation : editors, debuggers, other development tools. –Program execution : load, files, IO operations. –Access to IO devices: Read and writes. –Controlled access to files: protection mechanisms, abstraction of underlying device. –System access: Controls who can access the system. –Error detection and response: external, internal, software or hardware error. –Accounting: Collect stats., load sharing, for billing purposes.

6. B.Ramamurthy9/19/20156 Resource Manager u Processors : Allocation of processes to processors, preemption, scheduling. u Memory: Allocation of main memory. u IO devices : when to access io devices, which ones etc. u Files: Partitions, space allocation and maintenance. u Applications, Data, objects.

7. B.Ramamurthy9/19/20157 Processes u A program in execution, u An entity that can be assigned to and executed on a processes, u It is a unit of work. u Multiprogramming, time-sharing and real-time transaction systems lead to the refinement of the concept of process. u A process can be defined by its attributes and behaviors : it can be viewed as an Abstract Data Type (ADT). u When instances of this ADT co-exist we have concurrent processing. u Issues in concurrent processing : synchronization, mutual exclusion, deadlock, communication.

8. B.Ramamurthy9/19/20158 Memory management u Requirements: Process isolation, automatic allocation and maintenance, protection and access control, long-term storage facilities. u Virtual memory and file system facilities together satisfy all these requirements. u Virtual memory allows programs to address the memory from a logical point of view without regard to the amount of main memory available. u File : persistent storage for programs and data. u Can view file also as an ADT? File concept makes makes access control and protection convenient for the OS.

9. B.Ramamurthy9/19/20159 Protection and Security u When sharing resources, protection of the systems and user resources from intentional as well as inadvertent misuse. u Protection generally deals with access control. Ex: Read only file u Security deals usually with threats from outside the system that affects the integrity and availability of the system and information with the system. u Example: username, password to access system. Data encryption to protect information.

10. B.Ramamurthy9/19/201510 Scheduling and resource management u Scheduling and resource management is an Operations Research (OR) problem. u Goals : Efficient use of resources, satisfy the service time requested by a process, say, in a real-time system, fairness. u Short-term and long-term scheduling. u Queuing is one of the basic operations associated with scheduling. Interrupt is another important concept in the context of scheduling.

11. B.Ramamurthy9/19/201511 Operating system hierarchy Hardware + interrupts Virtual Mem Process + primitives Comm. Prmtvs File sys. Devices Directories Shell User processes

12. B.Ramamurthy9/19/201512 Types of OS u Multiprocessing - multiple CPUs u Multiprogramming - Time sharing, interactive u Real-time : deadlines, time constraints, predictability u Distributed systems : Sharing and fault tolerance, reliability, dependability. u Network OS u Network Transparent Systems : CORBA-like u Network-centric Systems : Jini-like

13. B.Ramamurthy9/19/201513 Structure of OS u Client-Server Model –SERVERS: Splitting the OS into parts, each of which handles one facet of the system, such as file service, process service, terminal service, or memory service –CLIENTS: User processes : A client process obtains services by sending messages to the servers. –Advantages: »Modularity : A bug in fileserver will crash only the fileserver and not the whole OS »Adaptability to distributed system: Services could be provided from a remote computer. »Example: Application Servers

14. B.Ramamurthy9/19/201514 Advances in Systems u Distributed Systems architecture has evolved quite significantly over the last three years with the advent of CORBA and Java. u Distributed Systems Technologies: DCE, CORBA, DCOM, Jini u Networked to Network-transparent to Network-centric Read Chapter 1 and Chapter 2