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Operating Systems


Lecture 12 Operating Systems (S&G, 6.4) – PowerPoint PPT presentation

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Title: Operating Systems

Lecture 12
  • Operating Systems
  • (SG, 6.4)

Read SG ch. 7,7.1 7.8(High-Level
Languages)for next week
Operating Systems
  • Wait for user requests
  • Launch programs (e.g., assemblers, loaders) to
    service those requests
  • Provide many other services to the user

(slide lt C. Hundhausen)
User Interface
  • Operating systems most important task Wait for
    user requests and process them
  • Receptionist
  • Dispatcher
  • The user interface performs this task

(slide adapted lt C. Hundhausen)
Text-OrientedUser Interface
  • Traditional user interfacecommand line
  • e.g., DOS, Linux, UNIX
  • gt cd mydocs/history
  • gt ls
  • gt ls al gt out.txt
  • gt grep "http" .html more

(slide adapt. lt C. Hundhausen)
GraphicalUser 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

(slide adapt. lt C. Hundhausen)
  • 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

(slide lt C. Hundhausen)
Encrypted Passwords
  • OS encrypts passwords so that they cant be
  • Encryption an active research area in computer
  • Need both encrypted text and algorithm for
    decoding it
  • Modern public key cryptography based on
    extremely large prime numbers

(slide lt C. Hundhausen)
File Access Permissions
  • OS restricts users from accessing the files of
  • 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 owners 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

(slide adapt. lt C. Hundhausen)
Hierarchy of File Access Permissions
  • Delete
  • Change
  • Append
  • Read

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

(slide lt C. Hundhausen)
Process Scheduling (2)
waiting ready running event
A, B, C D
D B, C
A, D C
B, D C
(slide adapt. lt UT Austin)
  • 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
  • B obtains printer, but is told that CD-ROM is not
  • Deadlock!
  • Both are waiting for a resource allocated to the
  • the only way to end the wait is for one of them
    to free the resource that the other needs

(slide lt C. Hundhausen)
Deadlock Prevention
  • How to prevent deadlock
  • If all resources needed by a program are
  • allocate the resources to the program
  • If not all resources needed by a program are
  • do not allocate any resources to the program
  • require the program to make a new request for
  • This algorithm would prevent deadlock in the
    preceding example
  • A and B both want to print a file located on
  • A requests CD-ROM and printer
  • A obtains CD-ROM and printer
  • B requests printer and CD-ROM. The request is
  • A finishes and releases CD-ROM and printer
  • B re-requests printer and CD-ROM
  • B obtains printer and CD-ROM
  • Deadlock is prevented!

(slide adapt. lt C. Hundhausen)
First Generation (194555)
  • 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!

(slide adapt. lt C. Hundhausen)
Second Generation (195565)
  • 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

(slide adapt. lt C. Hundhausen)
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

(slide adapt. lt C. Hundhausen)
Third Generation (1965-1985)
  • 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
  • If program has to pause for I/O, another program
    begins executing
  • Substantial improvements in CPU utilization were

(slide adapt. lt C. Hundhausen)
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 programs 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

(slide adapt. lt C. Hundhausen)
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
  • A given program is run for a designated time
  • When time slice is up or an I/O operation occurs,
    the CPU begins running another program
  • This proceeds in round-robin fashion

(slide lt C. Hundhausen)
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
  • This suggested that local computation was
    desirable, with remote access to more expensive
  • Return to single-user computer but with much
    better OS

(slide lt C. Hundhausen)
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

(slide adapt. lt C. Hundhausen)
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

(slide lt C. Hundhausen)
Future Generations
  • Multimedia, multimodal, and tangible user
    interfaces (speech, gesture, virtual reality,
  • 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

(slide lt C. Hundhausen)
Ad Hoc Networks
  • Wireless mobile communication
  • No fixed network structure (pattern of
  • 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

Smart Dust
  • Currently available motes
  • Bottle-cap size
  • 100200 each (1 in 5 years)
  • Sense temperature, light, motion, energy use,
    GPS, gas, pressure,
  • Set up ad hoc network
  • Battery lasts for years
  • 8K program memory, 512K RAM
  • coded in C, runs TinyOS
  • See Dust Inc. lthttp//www.dust-inc.comgt
  • Privacy issues?

(fig. lt IEEE Computer)
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