Operating Systems. Operating System A program running in a computer from the moment it is switched...
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Transcript of Operating Systems. Operating System A program running in a computer from the moment it is switched...
Operating System A program running in a computer from the
moment it is switched on. Part of the Systems Software of the computer. It is needed to control how the computer works
and to control any devices attached to the computer.
The CPU works much faster than its peripheral devices. The operating system co-ordinates all of the activities of a computer system so that the CPU is used efficiently.
For example Windows XP and MacIntosh OS 10.3.2
What does an Operating System do?
1. It checks all input devices: keyboard for key presses and mouse for movement and button presses.
2. It manages the sending of data to output devices like the screen and the printer
3. It controls where programs and data are placed in the main memory.
4. It manages the filing system5. In some network systems it controls the security
of the system.6. Provides a human computer interface (HCI) to the
user7. Lets the user know if any mistakes have occurred.
Summary of OS Functions Memory Management
Controls where data and programs are placed in memory.
File Management Organises data that is sent to backing storage
and controls the loading of files into memory. Input/Output
Controls input and output devices. Job Scheduler
Organises the way in which different tasks are carried out.
Error Reporting Informs the user if any problems occur.
Human Computer Interface Most computer systems use a graphical user
interface (GUI). One type of graphical user interface is a WIMP
system. The Operating System controls the way the WIMP system works. The user may choose to tailor or customise the WIMP system to suit their own preference.
Real Time Systems Immediate response. Provides accurate and up
to date information at any one time although many alterations are made continuously.
Examples:
Booking an aeroplane seat. If the information is not up to date then more than one person could book the same seat.
Guidance systems for rockets and space crafts. Monitoring equipment for nuclear or chemical plant.
Interactive Systems
An interactive system, used by most computers, responds immediately to user commands.
Example:
Bar code read at the checkout till gives the price and name of item.
Interactive Systems with Background Job Capability
Interactive operating systems can spend a large amount of time waiting for something to happen. Other tasks can be carried out in this idle time.
These tasks are called background jobs/tasks and are suspended as soon as the main task requires the processor.
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Example of Background Job
Most time in a word processor is spent waiting for characters to be typed in at a keyboard.
The OS can use these gaps to share out the processor between word processing and background printing.
The sending of data to the printer is carried out by the CPU in-between each key press.
This means that you don’t have to wait for the printer to finish before you can continue using the computer.
See Walsh page 273 for more info example
Device Driver A program which is an add-on to the
Operating System to allow the computer to operate a particular device which is attached to it.
Eg) if you buy a new printer, scanner or digital camera for your computer system then you will need to load a new device driver so that the device will operate correctly. This is usually supplied on a CD-ROM and must be loaded when the new device is installed for the first time.
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Printer Driver A printer driver takes the codes
used in the document and translates them into the appropriate code for the type of printer in use.
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Printers can produce many different printing styles such as underline, bold, italic, and different type faces such as Times New Roman, Courier, Comic Sans, Arial, Harrington, Chiller, Gigi
Before a printer can produce these styles, it must have the correct code sent to it from the computer.
The code which is required for any given style is different depending on the style of printer that is in use.
Eg) one code may produce bold print on a Brother laser printer and italic print on an Epson inkjet printer. A program driver program is used to overcome this problem.
Filing Systems The OS is responsible for the
information stored on backing storage.
It has to maintain information on: How many files there are Where the files are located on the disc How large the files are
Each time a file is modified, added or deleted the catalogue is updated.
Directories and Catalogues A catalogue is a list of all the files
or programs stored in a directory. A directory (folder) is an area on
backing storage where files are stored.
Data File Contains the data to be operated
on by programs or applications. Example: Text produced by a word
processing program.
Program File These contain the instructions
telling the computer what to do make a particular program or application work.
Example : Word Processing Programs like Microsoft Word, Claris Works etc.
Hierarchical Filing System This filing system allows different
levels to be set up and so files can be grouped together as the user wishes.
It is organised into sub-directories and folders.
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Example of Hierarchical Filing System
Root WordProcessing
Folder
Database
Folder
Spreadsheet
Folder
Diary
Moon
Soccer
Soccer
Soccer
Tables
Tables 2
File
Folder
Example of Hierarchical Filing System
ex1 ex2 ex3
W P
ex1 ex2
S S
S t G rd
W P S S D B
S 1
C om p u tin g
c irc les1 c irc les2 A rea
M ath s
G A th erton
D ia ry M oon S occer
W P
S occer Tab les Tab les2
S S
S occer
D B
C om p u tin g
K W in te rs
Ranger ServerFolder
Root
SubFolder
File
Advantages – Hierarchical Filing Systems Files can be organised better into
folders and sub-folders. Files can have the same names if
they are in different folders. Each folder will have fewer files in
it, so its easier to view the complete catalogue on screen at one time.
Disadvantages – Hierarchical Filing Systems
Easy to over-organise your work and have too many levels of folders, making it hard to find things.
More memory used.
Sequential + Direct (random) access devices
Tape = Sequential access as the data can only be read back in
sequence.
Disks = Direct access because thethe read/write head on thedisc can go straight to thetrack where the data is stored,
without having to read all the
data in between.
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