Lecture 12 2/19/04 13:43. Lecture 12. Operating Systems (S&G, 6.4) 2/19/04 CS Lecture Read S&G ch. 7, 7.1

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1 Lecture 12 Operating Systems (S&G, 6.4) 2/19/04 CS Lecture 12 1 Read S&G ch. 7, (High-Level Languages) for next week 2/19/04 CS Lecture 12 2 CS 100 1

2 Operating Systems Wait for user requests Launch programs (e.g., assemblers, loaders) to service those requests Provide many other services to the user 2/19/04 CS Lecture 12 3 User Interface Operating system s most important task: Wait for user requests and process them Receptionist Dispatcher The user interface performs this task 2/19/04 CS Lecture 12 4 (slide adapted < C. Hundhausen) CS 100 2

3 Text-Oriented User Interface Traditional user interface: command line e.g., DOS, Linux, UNIX > cd mydocs/history > ls > ls al > out.txt > grep "http" *.html more 2/19/04 CS Lecture 12 5 Graphical User Interface (GUI) Modern alternative: Graphical User Interface Pioneered by Apple Macintosh (1984) Windows, Icons, Menus, Pointer (WIMP) Directories represented by folder icons Files represented by specialized icons 2/19/04 CS Lecture 12 6 CS 100 3

4 Security In the 50s and 60s, physical security restricted access to computers and the files and programs they stored In modern times, that responsibility has shifted to the operating system Operating system controls access to computer by requiring users to log in with a username and password 2/19/04 CS Lecture 12 7 Encrypted Passwords OS encrypts passwords so that they can t be stolen Encryption an active research area in computer science Need both encrypted text and algorithm for decoding it Modern public key cryptography based on extremely large prime numbers 2/19/04 CS Lecture 12 8 CS 100 4

5 File Access Permissions OS restricts users from accessing the files of others Files can be set so that they are readable, writable, and executable by only a limited set of people, e.g.: Only the owner Only users in the owner s group Anyone Authorization lists maintain this information; they are encrypted so that they cannot be modified by unauthorized users OS prevents you from harming yourself 2/19/04 CS Lecture 12 9 Hierarchy of File Access Permissions Delete Change Append Read 2/19/04 CS Lecture CS 100 5

6 Process Scheduling Operating system ensures that the processor is being utilized efficiently While waiting for I/O operations to complete, the computer can do useful work This is done by maintaining a queue of processes (programs) to be run Programs have three status levels Running Ready Waiting 2/19/04 CS Lecture Process Scheduling (2) waiting ready running event A, B, C D D B, C A A, D C B B, D C A D reads a disk file A waits for keyboard input B writes to the printer; keystroke arrives for A Etc. 2/19/04 CS Lecture (slide adapt. < UT Austin) CS 100 6

7 Deadlock Operating system aims to prevent deadlock: a state in which no useful work can be done How deadlock happens (example) Programs A and B both want to print a file located on the CD- ROM A requests CD-ROM, then printer B requests printer, then CD-ROM A obtains CD-ROM, but is told that printer is not available B obtains printer, but is told that CD-ROM is not available Deadlock! Both are waiting for a resource allocated to the other the only way to end the wait is for one of them to free the resource that the other needs 2/19/04 CS Lecture Deadlock Prevention How to prevent deadlock If all resources needed by a program are available allocate the resources to the program If not all resources needed by a program are available do not allocate any resources to the program require the program to make a new request for resources This algorithm would prevent deadlock in the preceding example: A and B both want to print a file located on CD-ROM A requests CD-ROM and printer A obtains CD-ROM and printer B requests printer and CD-ROM. The request is denied A finishes and releases CD-ROM and printer B re-requests printer and CD-ROM B obtains printer and CD-ROM Deadlock is prevented! 2/19/04 CS Lecture CS 100 7

8 First Generation ( ) No operating systems Assemblers and loaders only Programmers themselves managed allocation of resources and execution of programs They signed up for blocks of time They brought in their punched card programs during their allocated block of time They manually loaded punched cards into computers They pressed buttons on console to initiate assembler translation process They manually loaded computer program into memory and began its execution This was a very tedious process! 2/19/04 CS Lecture Second Generation ( ) 1st generation systems often sat idle, because programmers spent a lot of their allocated time thinking and troubleshooting Led to development of batch operating systems Computer programmers hand in programs to computer operator, who runs collections of programs in batches 2/19/04 CS Lecture CS 100 8

9 Second Generation (2) Command languages introduced Enable programmers to specify to operating system what they want done Usually a mix of programs, data, and commands Role of operating systems as receptionist and dispatcher was born 2/19/04 CS Lecture Third Generation ( ) As computational speeds improved, it became unacceptable for computers to sit and wait for I/O operations The goal: Minimize CPU idle time Multiprogramming operating systems were born Many user programs loaded simultaneously into memory If program has to pause for I/O, another program begins executing Substantial improvements in CPU utilization were realized 2/19/04 CS Lecture CS 100 9

10 Third Generation (2) Issue: With multiple programs in memory, programs run risk of corrupting other programs by writing in their memory space Solution: Keep track of beginning and ending address of each program s memory space If a program attempts to reference/write to memory outside of its boundaries: report an error message shut down the program resume execution of another program 2/19/04 CS Lecture Third Generation (3) Time sharing systems emerged Took advantage of emerging network technologies Like multi-programming OS But programs do not have to be loaded into memory in advance Rather, programs can be loaded dynamically by users sitting at remote terminals; illusion of single-user computer Need for computer security emerged, because computer could now be accessed remotely Since many users accessed the computer simultaneously, I/O events could no longer be the only event that triggered a switch to a new program A given program is run for a designated time slice When time slice is up or an I/O operation occurs, the CPU begins running another program This proceeds in round-robin fashion 2/19/04 CS Lecture CS

11 Fourth Generation (1985-present) Personal computers became cheap and powerful enough that they could get work done more efficiently than a timeshare system At the same time, computer peripherals remained expensive This suggested that local computation was desirable, with remote access to more expensive peripherals Return to single-user computer but with much better OS 2/19/04 CS Lecture Fourth Generation (2) Network operating systems emerged Manages resources of local computer (client) Manages shared resources (servers) of a local area network (LAN) Typical servers include file, mail, and print 2/19/04 CS Lecture CS

12 Fourth Generation (3) Real-time operating systems Manage resources of embedded systems that are placed inside equipment (e.g., automobiles, airplanes, ovens, watches) Prioritizes requests, so that most critical ones are serviced first E.g., request for collision avoidance in an airplane would be serviced before request to turn up the heat in the cabin 2/19/04 CS Lecture Future Generations Multimedia, multimodal, and tangible user interfaces (speech, gesture, virtual reality, etc.) Issue commands via speech, gesture, interaction with tangible objects Parallel processing Distributed operating systems No boundaries between local area networks and global networks Users no longer need to be aware of where a resource is coming from Users can utilize global resources seamlessly as though they are local resources But, physical location is not irrelevant 2/19/04 CS Lecture CS

13 Ad Hoc Networks Wireless & mobile communication No fixed network structure (pattern of interconnectivity) Each node discovers & keeps track of which other nodes it can communicate with Messages are routed in accordance with current configuration of nodes Self-organize & adapt like social networks 2/19/04 CS Lecture Smart Dust Currently available motes : Bottle-cap size $100 $200 each Sense temperature, light, motion, energy use, GOS, gas, pressure, Set up ad hoc network Battery lasts for years 8K program memory, 512K RAM coded in C, runs TinyOS See Dust Inc. < Privacy issues? 2/19/04 CS Lecture CS

14 2/19/04 CS Lecture (fig. < IEEE Computer) CS