Lecture 2: Overview of Operating System

1. Lecture 2: Overview of Operating System Operating System Fall 2010

2. Outline • What is Operating System • OS as User/Computer Interface • Services provided by OS • OS as Resource Manager • Evolution of OS • Major Achievements of OS

3. What is Operating System? • An operating system is a program that controls the execution of application programs and acts as an interface between applications and the computer hardware. • Three objectives of operating systems: • Convenience • Makes a computer more convenient to use • Efficiency • Allows the computer system resources to be used in an efficient manner • Ability to evolve • Permit the effective development, testing, and introduction of new system functions without interfering with service

4. End User Programmer Operating- System Designer OS as User/Computer Interface Application Programs Utilities Operating-System Computer Hardware

5. Services provided by the operating systems • Program Development • OS provides a variety of facilities and services, such as editors and debuggers, to assist the programmer in creating programs. Typically, these services are in the form of utility programs that, while not strictly part of the core of the OS, are supplied with the OS and are referred to as application program development tools. • Program Execution • A number of tasks need to be performed before we can execute a program. Instructions and data must be loaded into main memory. I/O devices and files must be initialized, and other resources must be prepared. The OS handles these duties for the user.

6. Services provided by the operating systems (cont.) • Access to I/O Devices • Each I/O devices requires its own peculiar set of instructions or control signals for operating. The OS provides a uniform interface that hides these details so that the programmer can access such devices using simple reads and writes. • Controlled Access to File • The OS must provide protection mechanisms to control access to the files for different users. Certain files can read only, or write only, or execute only. The OS must enforce the access mechanism. • System Access • In the case of a shared or public system, the OS control access to the system as a whole and to specific system resources.

7. Services provided by the operating systems (cont.) • Error Detection and Response • A variety of errors can occur while a computer system is running • Internal and External hardware errors such as memory error, device failure, or malfunctions. • Software error such as arithmetic overflow or underflow, attempt to access forbidden memory locations • Operating system cannot grant request of application • Accounting • Collect usage statistic • Monitor performance • Used to anticipate future enhancement • prepare billing information

8. OS as Resource Manager Computer System I/O devices Memory OS Software I/O controller printers Keyboards etc. Programs and data I/O controller . . . I/O controller Auxiliary storage devices, disks, tapes … processor processor

9. OS as Resource Manager (cont.) • The OS is responsible for controlling and managing the various resources of a computer system. • The OS functions in the same way as an ordinary computer software, i.e., it is a program or suite of programs executed by the processor • The OS frequently relinquishes control of the processor and must depend on the processor to allow it to regain control • The OS itself doesn’t do any “useful” work.

10. Ease of Evolution of an OS • A major OS will evolve over time for a number of reasons: • Hardware upgrades plus new types of hardware • New services demanded by users • Fixer – fix holes in OS

11. Evolution of OS (1) • 1940-1950 • No operating system • Run as an open shop • User signs up for certain time to use it

12. Interrupt Processing Device Drivers Monitor Job Sequencing Control Language Interpreter User Program Area Evolution of OS (2) - Simple Batch Systems • mid 1950s - mid 1960s • User no longer has direct access to the machine • Submit the job to an operator who batches the jobs together sequentially and places the entire batch on the input device • Often jobs of a similar nature can be bundled together to further increase economy

13. Evolution of OS (2) - Simple Batch Systems (cont.) • Job Control Language (JCL) • Special type of programming language • Provide instruction to the monitor $JOB user_spec ; identify the user for accounting purposes $FORTRAN ; load the FORTRAN compiler source program cards $LOAD ; load the compiled program $RUN ; run the program data cards $EOJ ; end of job $JOB user_spec ; identify a new user $LOAD application $RUN data $EOJ

14. Evolution of OS (2) - Simple Batch Systems (cont.) • Need additional hardware features to support the batch OS: • Memory Protection – protect the OS from being wiped out • Timer – prevent the job run infinitely • Privileged Instruction • certain instruction can only be executed by OS, and not by user. • I/O could only be performed in monitor (supervisor) mode, • CPU runs in supervisor mode or user mode • Interrupts • early models did not have this capability. • Later models have. • Make more efficient use of resources Note: Some memory is given to OS and some processor time is given to OS. But we are still better off because machine is a lot faster than human operation.

15. Monitor (more like a operating system) User program 1 User program 2 User program 3 User program 4 Evolution of OS (3) - Multiprogrammed Batch Systems • 1960s - present • Several users are in memory at the same time • Match I/O intensive job with CPU intensive job • Important to have Interrupt-Driven I/O or DMA to support multiprogrammed batch system.

16. Uniprogramming • Processor must wait for I/O instruction to complete before preceding

17. Multiprogramming • When one job needs to wait for I/O, the processor can switch to the other job

18. Multiprogramming

19. Evolution of OS (4) - Time-Sharing Systems • 1970s - present • To support interactive computing • In a time-sharing system, multiple users simultaneously access the system through terminals, with the OS interleaving the execution of each user program in a short burst or quantum of computation. • Context Switching • A job (now often called process) can get “switched in” or “switched out”. • OS should give the illusion for the process as if it exists in the CPU continuously

20. Batch Multiprogramming versus Time Sharing

21. Evolution of OS (5) • Real-time computer • Execute programs that are guaranteed to have an upper bound on tasks that they carry out. • e.g. guided missile systems, medical monitoring equipment • Multiprocessor – have more than one CPU • Shared memory multiprocessors • Access the same memory - memory access must be synchronized • Distributed memory multiprocessors • Each CPU has its own associated memory – communication between processors is often slow and complicated • Networked/Distributed Systems – consist of multiple computers • Networked systems: users are aware of the different computers that make up the system • Distributed systems: multiple computers are transparent to the user.

22. Major Achievements of OS • OS are the most complex software ever developed • In the last several decades, we have made several theoretical advances in the development of OS: • Processes • Memory management • Information protection and security • Scheduling and resources management • Systems structures

23. Processes - Definition • The concept of process is fundamental to the structure of OS. Many definitions have been given: • A program in execution • An instance of a program running on a computer • The entity that can be assigned to and executed by a processor • A unit of activity characterized by a single sequential thread of execution, a current state, and an associated set of system resources.

24. Processes • In a multiprogrammed systems, many jobs are in progress at the same time. It became impossible to analyze their interactions. Therefore, there are many source of errors: • Improper Synchronization • It is often the case that a routine must be suspended awaiting an event that occurs elsewhere • Failed Mutual Exclusion • Certain shared resources can only be used by one user at a time • Nondeterminate Program Execution • The results of a particular program should depend only on the input and not on the activities of other programs in a shared system • Deadlocks • It is possible for two or more programs to be hung up waiting for each other • We need to tackle these problems in a systematic way. The concept of the process provides the foundation.

25. Processes - Components • We can think of a process as consisting of three components: • An executable program • The associated data needed by the program • The execution context of the program • All information the operating system needs to manage the process

26. CPU registers process list PSW OS PC Base b Limit h Context process A Data PC Instructions other registers PC … Context process B PC Data Instructions Processes

27. Memory management • Process isolation • The OS must prevent independent processes from interfering with the data and memory of each other • Automatic allocation and management • Programs should be dynamically allocated across the memory hierarchy as required. • Support for modular programming • Protection and access control • Sometimes it is desirable to share data. Sometimes it is not. The OS must enforce them • Long-term storage

28. Virtual Memory • Allows programmers to address memory from a logical point of view • While one process is written out to secondary store and the successor process read in there in no hiatus

29. File System • Implements long-term store • Information stored in named objects called files

30. Paging • Allows process to be comprised of a number of fixed-size blocks, called pages • Virtual address is a page number and an offset within the page • Each page may be located any where in main memory • Real address or physical address in main memory

32. Main Memory Processor Memory Management Unit Virtual Address Real Address Disk Address Secondary Memory Virtual Memory Addressing

33. Information Protection and Security • Access control • Regulate user access to the system • Information flow control • Regulate flow of data within the system and its delivery to users • Certification • Providing that access and flow control perform according to specifications

34. Scheduling and Resources Management • A key task of an OS is to manage the various resources available to it and to schedule their use by the various active processes. • Any scheduling policy must consider three factors: • Fairness • Give equal and fair access to all processes • Differential Responsiveness – priorities • Discriminate between different classes of jobs • Efficiency • maximize throughput, minimize response time, and accommodate as many uses as possible etc.

35. System Structure • Early OS are monolithic • Later OS are modular • View the system as a series of levels • Each level performs a related subset of functions • Each level relies on the next lower level to perform more primitive functions • This decomposes a problem into a number of more manageable subproblems

36. System Structure (cont.) • Microkernel architecture • assigns only a few essential functions to the kernel • address space • interprocess communication (IPC) • basic scheduling

37. System Structure (cont.) • Modules • Most modern operating systems implement kernel modules • Uses object-oriented approach • Each core component is separate • Each talks to the others over known interfaces • Each is loadable as needed within the kernel • Overall, similar to layers but with more flexible

38. Solaris Modular Approach

39. Operating System Design Hierarchy

40. Operating System Design Hierarvichy (cont.)

41. Operating System Design Hierarvichy (cont.)

42. End Thank you!