COMP091

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COMP091 Operating Systems 1

• My Name Prof. Baker
• Web Page http//fleming0.flemingc.on.ca/chbaker
  
• Lecture notes and assignments will be posted to
  the web page
• Email cmb-ssfc_at_fivefortyfour.com
• Or charles.baker_at_flemingcollege.ca
• Assignments are to be submitted as email
  attachments

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COMP091 Operating Systems 1

• History of Operating Systems

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Generations

• First Generation
• No OS as we know it
• Second Generation
• Batch processing
• One job at a time
• Third Generation
• Multi-programming
• Spooling
• Fourth Generation (now)
• Massive interactivity
• GUI
• Programming by system calls

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In the very early daysvon Neumann Architecture

• John Louis von Neumann, Hungarian mathematician
  28 December 1903 - 8 February 1957
• Proposed the stored program concept
• Program instructions stored in memory along with
  data
• Rather than being wired on plug boards
• Circuitry decodes instructions
• Just have to get code into memory

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In the very early daysProgramming

• Computers had rows of switches representing bits
• Address row contained address in binary
• Data row contained content in binary
• Load button caused data to be loaded into address
  in memory
• Programming meant setting the address switches,
  then the data switches, then pressing "load"
• Repeat for each instruction and data address

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In the very early daysOperating

• After loading all the instructions and data,
  program had to be started
• Computer had a "Run" button
• "Run" button set next instruction counter to
  first memory location and started execution of
  instructions there
• "Run" button was the entire operating system
• But it introduced the modern operating system
  concept of Boot Loaders

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Boot Loaders

• Does not mean boot as in kick as in kick start
• Refers to old expression "Pull yourself up by
  your boot straps"
• Of course that can't be done because who has
  straps on their boots
• But the idea of a program that gets loaded
  without the help of some other program is
  reminiscent of this
• Hence the bootstrap program, or boot loader
• The "run" button was the first boot loader

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In the very early daysAutomatic Programming

• Programming by switches very tedious and error
  prone
• Eventually programs were coded onto paper tape
  using a paper tape machine with a keyboard
• "load" button could read entire program from
  paper tape into memory ready to run
• This was referred to as automatic programming
• Some though it would spell the end for
  programmers
• Introduced first modern OS component
• device drivers

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Device Drivers

• First device drivers were necessary to control
  the devices that contained the programs
• These were supplied by the computer manufacturer
  and at first were hard wired
• Programmers wrote their own drivers to interact
  with hardware at run time, after booting was
  finished
• Manufacturers drivers were just for booting
• Eventually this duplication of effort led to
  another modern concept
• Runtime Library

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Runtime Libraries

• Early run time libraries were essentially open
  source creations
• Programmers shared common code among themselves
• Later, manufacturers began distributing runtime
  libraries with their computers
• Made machine more usable
• Maybe ensured efficient use
• Library routines were linked to programs by link
  editor after compiling or assembling

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I/O Control Systems

• On early systems programs directly controlled I/O
  devices using custom code (maybe shared in a
  library)
• Eventually manufacturers made their I/O libraries
  available at run time as an I/O Control System
• Part of main memory was set aside for the IOCS,
  the rest of memory was for users
• This was the first development to resemble on O/S
• It introduced the idea of Memory Management
• And made OS functions available at run time

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In the very early daysComputer Operators

• Automatic programming also introduced the idea
  of the Computer Operator
• Programmers would fill out a form specifying
  their run time requirements
• Run request form, along with paper tape, card
  deck or magnetic tape(s) would be handed to
  operator to run when computer became available
• Programmer didn't need to be there at run time to
  set switches

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Computer OperatorsScheduling

• Computer operators scheduled jobs into computers
  one at a time
• Early job queues consisted of stacks of Job
  Request forms, maybe clipped to a clothes line
• Users were charged for use of computer time, and
  for use of peripherals
• Operators would keep track of this info on the
  Job Request Form, but a more efficient method was
  desirable
• Especially from the accountants' point of view

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Second Generation -- Monitors

• The IOCS was in memory and active at run time
• And was involved in I/O operations as well as
  starting and stopping jobs
• So accounting was added to the IOCS to allow
  accurate billing for machine time and I/O
  utilization
• These systems now came to be called monitors and
  signaled the start of the second generation of
  operating systems
• And introduced the OS concept of Accounting

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Accounting

• Accounting is still present in modern multi-user
  operating systems as part of the Security System
• Security systems are concerned with identity and
  that means
• Identification
• Who are you
• Authentication
• How do we know
• Authorization
• What can you do
• Accounting
• How much of it did you do

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Better Scheduling

• With operators manually scheduling jobs, there
  would be idle time between jobs while the
  operators set up the next job
• This wasn't a problem if jobs ran for a long time
• The idle time was small relative to the
  productive time
• With faster computers, jobs ran faster and the
  idle time became significant
• The solutions was another modern operating system
  concept The job queue

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Batch Operating Systems

• With the addition of a job queue to the monitor,
  more efficient scheduling became possible
• Jobs would be read into a job queue when they
  were submitted
• The monitor would start the next job as soon as
  the last job finished
• Jobs' resource needs would be described by Job
  Control Language statements stored on the queue
  with the job
• These batch OS systems were the first real OS's

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Some Examples

• Monitors
• FORTRAN Monitor System, General Motors Operating
  System, Input Output System
• Batch Systems
• Note that these OS were almost all supplied by
  the computer manufacturer
• GECOS, SCOPE (Supervisory Control of Program
  Execution - CDC), EXEC (Univac) , MCP
  (Burroughs), IBM 1410/1710 OS

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2nd Generation Problem

• In 2nd generation OS only one program could run
  at a time
• If that program was waiting for I/O the entire
  machine would be idle
• But if the monitor could hand the machine to
  another job while the first one waited the idle
  time wouldn't be wasted
• This introduced another modern concept
• Multiprogramming
• More than one job loaded and ready to run

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Another Problem

• Multiprogramming OS's switched jobs when one
  became idle
• But on-line users didn't want to wait long times
  for all other users to go idle
• Interactive users required time slices on a
  regular basis
• A time sharing OS would stop jobs after a short
  period of time to give some time to other users
• Everyone had the illusion of a computer available
  for their exclusive use

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Third Generation Multiprogramming

• The third generation of Operating Systems was
  characterized by multiprogramming capabilities
• Multiple jobs loaded in memory and ready to run
• OS passes control to another job when one goes
  idle
• Timesharing systems allocate regular time slices
  to interactive jobs so none will be inactive for
  unacceptable periods of time

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Third Generation Memory Partitions

• Multiprogramming required that many jobs be in
  memory at once
• This required the modern OS capability of memory
  partitioning
• OS divides memory into partitions
• Allocates a partition to each job
• Memory Maps map relative addresses into
  partitions' real addresses so jobs don't need to
  know where they are actually loaded
• Originally fairly static mapping

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Third Generation Virtual Memory

• With multiprogramming there could be many jobs
  loaded in memory at once, and the more there were
  the more efficiently the machine resources could
  be deployed
• Soon memory just wasn't large enough to hold
  enough jobs to keep the increasingly faster CPU's
  supplied with work
• Virtual memory solved this by temporarily moving
  idle jobs from memory to disk until it was time
  to reactivate them

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Third Generation Thrashing

• Moving jobs (or portions called pages) from real
  to virtual memory came to be called paging
• It allowed more jobs to be available to use the
  CPU resources
• But it also consumed resources
• If the resources used by paging was too much
  resource nothing would get done
• This condition is called thrashing
• Efficient paging algorithms seek to prevent
  thrashing

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Thrashing Example

• In the 1970's IBM sold an operating system called
  System 370
• It was a multiprogramming virtual memory batch OS
• They also sold VM, (Virtual Machine) which
  allowed customers to run more than one IBM OS at
  the same time
• In one case a thrashing S370 system was resolved
  by running the S370 OS under VM
• VM had a more efficient paging algorithm

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Third Generation Spooling

• Another problem introduced by multiprogramming is
  that you can't time share a printer
• Jobs would be intermixed on the paper
• 2nd generation OS gave jobs exclusive control of
  I/O devices like printers
• 3rd generation introduces spooling
• Printed output intercepted by OS and stored in a
  disk file called a spool, or print queue
• Tanenbaum says SPOOL Simultaneous Peripheral
  Output On Line
• Complete print jobs are sent to printer (or other
  device) when the generating job is finished

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Third Generation File Systems

• Early disk drives had removable disk packs and
  tape drives
• Users handled them in whatever way they wished,
  addressing the hardware in hardware terms
• With larger disks, and the use of disk space by
  the OS for spooling, job queues, page files etc,
  it became desirable for disks to have a common
  format
• Users would use space on these permanently
  mounted system disks, facilitating scheduling
• The now familiar hierarchical file systems were
  introduced to enable sharing of space on system
  disks

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Third GenerationProcesses

• Originally the granularity of multiprogramming
  was at the level of a complete job
• With virtual memory it became more efficient to
  swap pages rather than jobs
• Also, jobs spent a lot of time using system calls
  to accomplish objectives and that involved
  processes running in the memory space of the OS
• It became necessary to start and stop processes
  rather than jobs leading to the modern OS concept
  of processes

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Third GenerationThreads

• Jobs running in a modern OS can start processes
  that run in the memory of the OS, using drivers
  or other functions available through system calls
• Each process shares the memory where the code
  resides, but is allocated separate memory for
  data, including state information
• Each of these processes represents a process
  thread through the memory of the shared code
• The shared code is multi-threaded

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Third GenerationScheduler

• Scheduler Adds new processes to the process
  table and removes completed processes from the
  process table
• Process table contains
• Memory area assigned to the process
• Priority of the process
• State of the process (ready or waiting)

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Third GenerationDispatcher

• Dispatcher Controls the allocation of CPU (of
  time slices) to the processes in the process
  table
• The end of a time slice is signaled by an
  interrupt.
• Each process is allowed to execute for one time
  slice
• It performs "process switch" - procedure to
  change from one process to another
• ProcessA -gt Dispatcher -gt ProcessB

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Other 3rd Generations Issues

• Deadlock
• If process A waits on process B while process B
  waits on process A neither will ever complete
• This is called deadlock
• 3rd generation OS had to learn to detect and
  prevent deadlock
• Security
• With so many processes on the same machine OS had
  to learn how to keep them separated

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4th Generation

• Generally considered to be the OS's that operate
  modern desktop computers
• Windows, Linux Android, and a few others
• Massive reliance on OS system calls
• Ubiquitous networking
• Essentially Interactive

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Resources

• http//www.personal.kent.edu/rmuhamma/OpSystems/M
  yos/osHistory.htm
• http//en.wikipedia.org/wiki/History_of_operating_
  systems
• http//www.osdata.com/kind/history.htm

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Marking Scheme and Course Outline

• Lectures and lab assignments posted at
• http//fleming0.flemingc.on.ca/chbaker/
• Marking scheme as follows
• Two tests weeks 7 and 15 _at_ 15
• Lab test 10
• 10 labs at 5
• Professionalism and comprehension 10