Transcript System Software

Computer Systems
2009-2010
Week 12: System Software
Alma Whitfield
Session Aims
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Understand what System Software is
Operating System as an example of
System Software
Functions of an operating system
Study of operating system process
management function
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Need for system software
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Computers very complex
Come with large bundles of software to
help the non-specialist
This software is called system software
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Software types
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System software
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operating systems
language translators (e.g. Java language)
Application software
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programs we buy (sometimes and use) e.g.
Microsoft Word, Powerpoint, web browsers,
games.
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Operating systems
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In this session we focus on the most
important kind of system software – the
operating system
Examples of operating systems include
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MS-DOS
Windows
Linux
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What an operating system does
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Just like
mother
Teenager
does not
know how to
operate
toaster etc ..
… but mother
does
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What a mother does
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Teenager makes
service call
Mother responds by
controlling the
device needed
When device done it
interrupts mother
Mother responds
by delivering output
to teenager
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What an operating system does
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Alternative would be to have the teenager
understand how to work all the hardware
Not regarded by teenager as efficient!
Computers are invented by teenagers
Can you see where this is heading?
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What an operating system does
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Who is mother
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Operating system
Who is the
teenager
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Application
program
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Tasks carried out by an
operating system
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Running programs
Managing files
Managing main memory
Controlling peripherals
Utility programs
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Running programs
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User requests a program
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This triggers a sequence of actions
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mouse click
program name at command line
ensure program is in main memory
start fetch execute
manage program’s file access
manage program’s I/O device access
Operating system can detect and respond to errors
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end a program after illegal attempt to access memory
retry an operation when device not ready
recover after power failure
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Managing files
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Programs and data saved on disc as files
Operating System file manager
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organises files
enables user to add, update delete files
controls file ownership in shared system
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e.g. network, mainframe
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Managing main memory
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Managing memory space
Simultaneous programs
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must not interfere with each other’s space
Large programs
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possible to load only required parts
may use overlays
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e.g. Word with little used menu options
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Controlling peripherals
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Operating
system
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includes
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kernel
drivers
Drivers
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plug and play
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Kernel
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The kernel is a key portion of the Operating
System that is loaded into memory when the
machine is switched on and remains constantly
in memory.
Contains the programs to handle the most
frequent commands
The kernel is also know as the nucleus
Good performance by the kernel is very
important for good performance by the
machine
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Utility programs
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Editors
Clock
Calculator
Calendar
Whatever else those nice guys at
Microsoft can think of
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Issues over System Software
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What constitutes an operating system?
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e.g. should it include Web browser, Java Virtual
Machine and media player?
Microsoft was taken to court in the United
States for anti-competitive conduct in making
Internet Explorer 4.0 (and a non-standard JVM)
non-removable parts of Windows 98
In 2004 the European Commission ruled that
Microsoft broke EU competition law in tying
Windows Media Player to its operating system
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Do we need an Operating System?
Is the statement below True or False ?
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You can’t use a computer without an
Operating System!
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False
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You can use a computer without an
operating system.
However, you must be highly skilled in
Electrical and Mechanical Engineering
Some of the very first computers did not
have Operating Systems
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Studying the tasks carried out
by an operating system
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Running programs
Managing files
Managing main memory
Controlling peripherals
Utility programs
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Studying the tasks carried out
by an operating system
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Running programs
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Managing files
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Week 14
Controlling peripherals
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done in Week 10, 11
Managing main memory
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today (Week 12)
Week 13 (hard disk)
Utility programs
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Running programs
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Running programs
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First machines
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single user
single program running at a time
uniprogramming
More modern machines
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multiple users
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each user perhaps running several programs at
same time
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e.g. bank system
e.g. Windows PC
multiprogramming
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Uniprogramming
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No Operating System
Machines run from a console with display
lights and toggle switches, input device
and printer
Scheduling time was an issue because
one job had to finish before another
could start
CPU must wait for I/O instructions to
complete before proceeding
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Programming with a female
operating system
The girls organise the
loading and running of
programs.
They are effectively the
1940s version of the
modern operating
system
http://www.berkeleyprep.org/webhouse/bh/html/histpic.htm
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ENIAC (Electronic Numerical
Integrator and Computer) 1946
Men occasionally
involved as well!
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ENIAC (Electronic Numerical
Integrator and Computer) 1946
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... was the first large-scale, electronic,
digital computer capable of being
reprogrammed
cost $500,000
only operational for 5 months before it
had to be shut down for refurbishment
and a memory upgrade
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Uniprogramming
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Multiprogramming
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Multiple users accessing the same data
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e.g. bank system
Single user running several programs at
the same time
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e.g. Windows PC
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Multiprogramming – two main
issues
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Sharing the processor
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how can two programs be fetching and
executing at the same time in the same
CPU?
Sharing the main memory
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how can we avoid the different sets of
program instructions and data in main
memory getting mixed up?
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Multiprogramming – two main
issues
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Sharing the processor
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Today
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how can two programs be fetching and
executing at the same time in the same
CPU?
Sharing the main memory
how can we avoid the different sets of
program instructions and data in main
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memory getting mixed up?
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Sharing the processor
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Original problem:
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expensive , fast CPU waiting for slow
peripherals – uneconomic
Solution
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have CPU run another program while waiting
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Other advantages
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Carry out tasks simultaneously
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Share peripherals
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Mainframe and minis can centralise printers etc
Dumb terminals are cheap
Share data
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E.g. control central heating and word process
Users can access same files
Concurrent programs on same machine
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This is how we use Windows
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Disadvantages
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Breakdowns affect everybody
Portability – need link to central machine
Expense – but getting cheaper
Security risks
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Switching between programs
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Done by the kernel (part of operating
system)
Known as a context switch
Each program needs a control block
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Preserves program’s state
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CPU register contents
Which data files are opened
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Different strategies for switching
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When program finished or blocked
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Simple to implement
But, programs can hog the processor
At regular intervals (time slicing)
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Programs cannot hog processor
But, complex to control so time overhead
This is the strategy in common use
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Time slicing
Blocked programs (waiting
for a peripheral) are not
allocated time slices
Each interval is a
time slice
Scheduling – deciding which program runs next
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Running programs are
“processes”
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Processes consist of:
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The program (set of instructions)
Current state of data structures
Current state of CPU registers
Which I/O devices currently open
Which files are currently open
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Process Creation
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Parent processes create children processes,
which, in turn create other processes, forming
a tree of processes
Resource sharing alternatives
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Parent and children share resources
Children share subset of parent’s resources
Parent and child share no resources
Execution alternatives
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Parent and children execute concurrently
Parent waits until children terminate
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Process states
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Running
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Ready
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During its timeslice
While some other process is running
Blocked
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Unable to proceed e.g. waiting for input
device
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Changing Process States
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ready/waiting
running
blocked
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Context switching
with interrupts
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Interrupt
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Signal to CPU to
stop what it is
doing and execute
an interrupt
routine
Clock interrupt
generated by clock
at fixed intervals
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Scheduling Algorithms
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A scheduling algorithm is the method
by which processes are given access to
processor time.
e.g.
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Round Robin
Fair Queuing
FIFO
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Lots of Scheduling Algorithms
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A
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C
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D
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E
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F
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Anticipatory scheduling
Atropos scheduler
CFQ
Critical path method
Deadline-monotonic scheduling
Deficit round robin
And so forth
Earliest deadline first scheduling
Elevator algorithm
FIFO
FINO
Fair Queuing
Fair-share scheduling
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What have we covered?
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Characteristics of System Software
The responsibilities of Operating System
The KERNEL
Uniprogramming and Multiprogramming
Context Switching
What makes a process
How Processes are managed
CPU allocation and Scheduling Algorithms
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Round 1
Which of the following best describe the
purpose of an Operating System?
a)
b)
c)
d)
To
To
To
To
make the computer easy to use
ensure hardware is used efficiently
store data.
execute program instructions.
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Round 1
Which of the following best describe the
purpose of an Operating System?
a)
b)
c)
d)
To make the computer easy to use
To ensure hardware is used efficiently
To store data.
To execute program instructions.
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Round 2
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Which of the following are operating
systems:
1.
2.
3.
4.
5.
6.
Unix
Visual Basic
Pascal
Pie Eater
Windows
Linux
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Round 2
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Which of the following are operating
systems:
1.
2.
3.
4.
5.
6.
Unix
Visual Basic
Pascal
Pie Eater
Windows
Linux
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Round 3
Which of the following best describe the
responsibilities of an Operating System?
a) To Manage Resources
b) To store data.
c) To execute program instructions.
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Round 3
Which of the following best describe the
responsibilities of an Operating System?
a) To Manage Resources
b) To store data.
c) To execute program instructions.
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Round 4
Which of the following best describes the
KERNEL?
a) The centre of the Operating System
b) The part of the Operating System that
remains resident in memory
c) The execution element of the Operating
System
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Round 4
Which of the following best describes the
KERNEL?
a) The centre of the Operating System
b) The part of the Operating System that
remains resident in memory
c) The execution element of the Operating
System
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Round 5
Which best describes Multiprogramming
Operating Systems?
a) The ability to process multiple applications
at once
b) The ability to give the impression that it is
processing multiple applications at once
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Round 5
Which best describes Multiprogramming
Operating Systems?
a) The ability to process multiple applications
at once
b) The ability to give the impression that
it is processing multiple applications
at once
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Round 6
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Context Switching can best be described
as:
a) Switching from one CPU to another in a
Dual Core Processor
b) Saving the state of a process and loading
the state of another process
c) Switching from one Multiple Simulation to
the next
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Round 6
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Context Switching can best be described
as:
a) Switching from one CPU to another in a
Dual Core Processor
b) Saving the state of a process and
loading the state of another process
c) Switching from one Multiple Simulation to
the next
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Round 7
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Windows will work on an Apple Macintosh
because the computer architecture is
similar.
TRUE or FALSE ?
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Round 7
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Windows will work on an Apple Macintosh
because the computer architecture is
similar.
FALSE
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Next Week
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Hard disc management
Quiz in your seminar which is TIMED.
You should also be working on the
research in relation to your presentation
assignment
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Additional Reading
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O’Gorman J (2000) Operating Systems
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References
Coustan D, Franklin C How Operating Systems Work [online] http://Computer.Howstuffworks.com
[Accessed 10-1-2011]
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