Transcript Supporting Software

Reminder – Supported Study & Oct Test Fri 31
Outline
• Calculation Questions
• October Test Revision
Learning Objectives
By the end of the lesson I will be able to:
• Discuss the need for the operating system
• Explain the role of the bootstrap program
• Discuss the 5 functions of the operating systems
Systems Software
Computer hardware would be useless without software, the
lists of instructions which tell the hardware what to do.
Computers require various types of software to make them
useful. These can be classified as follows:
1. Operating System
2. Utility software
3. Applications software
Operating System
The operating system (OS) is the piece of software required by
the computer to make sure that it works correctly and efficiently.
Manage the computer and allows the user to communicate with
the hardware and software.
Modern operating systems are typically stored on Hard disk and
loaded into RAM when the computer is switched on.
Storing the OS on disk means that it can be easily updated.
Windows XP is updated on a daily basis.
Bootstrap program (Bootstrap Loader)
The bootstrap program can be used to start the computer, and
in doing so:
• Clear the memory
• Checks hardware
• Locate and load the Operating System into RAM
Bootstrap program is held in ROM.
The main part of the operating system in RAM manages the
computer and allows the user to communicate with the
hardware
Functions of the operation system:
• Interpreting User Commands
(Command Language Interpreter)
• File Management
• Memory Management
• Input/Output Management
• Managing Processes (kernel)
• Resource Allocation
Interpreting user commands – Command Language Interpreter
This part of the operating system accepts commands (from a
keyboard, mouse, etc) and passes them to the appropriate parts of the
operating system.
User Interface (Command Language Interpreter)
The layer with which the user interacts in order to give instructions to
the computer.
Types of Interface:
• Command Driven
• Menu Driven
• Graphical User Interface
File Management System
Organises and tracks how files are stored on backing storage.
Concerned with the efficient use of the computers backing storage
devices and media. It allocates blocks of data to particular areas on
the backing storage medium (Hard Disk).
If you give a command to load a file from disk, the Command
Interpreter will pass this instruction to File Management.
Storage Medium
• Hard Disk
• CD-ROM
• DVD-ROM
• USB Flash Pen
File Management Functions:
• Holds details of where the files are stored. This information is
held in a disk catalogue.
• Requesting transfers of data from the input/output devices.
• Organises files in a hierarchical filing system, which will store
files in separate directories and sub-directories.
File Management cont…
File Management uses its index (catalogue) to work out exactly
where on the disk the file is stored. e.g. Track 10, Sector 4.
File Management also maintains the security of the files. Included
with the file information are the access rights for users. e.g. read
only.
When a file is to be loaded, File Management will pass the
information about the physical location (e.g. Track 10, Sector 4) to
Input/Output Management.
Memory Management
Controls where programs and data are placed in main memory.
Functions:
1. Checks to make sure that there is enough free space to store the
new program and data.
2. Allocates an area of RAM
3. Load program into RAM making sure that programs do not access
RAM space allocated to other programs
4. Monitoring the use of memory. Ensure programs do not interfere
with the area of memory used for the OS.
5. Frees memory locations when data is no longer needed.
Input/Output Management
It is the task of Input/Output Management to do all the actual data
transfers and issue the appropriate control signals to the peripheral
devices.
How it Works.
When a file is to be loaded, File Management will pass the
information about the physical location (e.g. Track 10, Sector 4) to
Input/Output Management.
Input/Output Management has to send the correct signals to the Hard
Disk to tell it to access Track 10, sector 4, read the data and send it to
RAM.
Input/Output cont…
Different types of peripheral devices work in different ways.
Hard Disk Drives, CD Drives, DVD drives, solid state storage devices,
inkjet printers, laser printers, CRT monitors, LCD monitors are all very
different.
Input/Output Management has to know how to communicate with
each device to allow data transfer to take place.
Device manufacturers provide drivers (small programs) which are
installed and become part of Input/Output Management. These allow
communication to take place.
Managing Processes (kernel) – heart of the OS
Process is an instructions in execution.
Modern OS will typically have several processes on the go at the
same time.
e.g. Operating system, Microsoft Word, Virus Checker
Processes have to share processor time. The OS has to manage the
processes so that they can be carried out efficiently and effectively.
It provides an environment in which processes can exist.
Functions
1. Loaded into RAM and stays there, while other pieces of the OS are
loaded in and out of memory.
2. Decides which process is allowed and how long needed (schedules
CPU time).
3. Maintains the reliability of the process by keeps a note of the state
of each process and makes sure that each process is getting its fair
share of processor time.
4. Handles and implements interrupts (Terminates process and
restores system).
Resource Allocation
The competing processes require access to resources.
Resources include the processor, RAM and Input/Output devices. If
one process is in the middle of sending data to the hard disk then
another process cannot be allowed to start sending its data there too
until the first process has completed its task.
The OS has to manage the resources by controlling how and when the
processes are to be allowed to use them.
Making the most of the attached devices and getting them to work at
their highest useful rates.
Utility Programs
Designed to carry out specific tasks related to the management
or maintenance of a computer system.
Examples of utilities:
 Anti-Virus Checker
 Disk Editor
 Disk Defragmenter
 System Restore
 Disk Clean up
 File Compression
Virus Checker Virus checking software should be able to
detect the occurrence of a virus infection and remove it from a
computer.
Virus - Revision
A program written with the deliberate intention of causing
damage to a computer system.
• Email Attachments
• Internet
• Sharing of floppy disk
Remember – a virus can only be activated if you execute it.
For example, opening the attachment from an email or clicking
on an executable file on the internet.
How a virus Operates
A virus is a program or programming code that replicates by being
copied or initiating its copying to another program, computer boot
sector or document.
Operations of the Virus Checker
A virus checker examines a computer system to find virus software.
It can be set to examine any type of backing storage media, check
email attachments and files downloaded from the internet.
A good virus checker will constantly work in the background checking
for signs of virus activity.
A Virus Checker uses many techniques to detect a virus within a
computer system. (Will Cover)
Disk Editor
Allows the user to read, edit, and write to low-level raw data on the
hard disk.
It can be used to repair/reconstruct damaged files and directories.
Gives the user complete power over the contents of every block
(sector) on the disk so considerable knowledge and care is needed.
It would be very easy for an inexperienced user to cause serious
damage to the contents of a hard disk by altering bytes of data on the
disk.
Disk Defragmenter
Read/write to Hard Disk – How it all works
Magnetic disks are organised so that they store data in blocks of a
fixed size.
Depending on its size, a file will typically occupy several blocks.
Normally data is stored in consecutive blocks on the disk.
This makes sense as the Read/Write head moves to the required
track and starts to read the consecutive blocks.
After a time, the disk starts to fill up and files are edited and deleted.
The remaining free blocks are not necessarily next to each other.
When new files are saved the blocks may be on different parts of
the disk.
It then takes longer to access these files.
This is called file fragmentation.
A defragmenter program is a utility which reorganises the data on
the disk so that all blocks for a file are stored together to improve
access times.
This should be done regularly to maintain hard disk performance.
(Especially if nearly full)
System Restore
System Restore works a lot like the Undo command in Microsoft Word.
You can use System Restore to remove any system changes that
were made since the last time you remember your computer working
correctly.
System Restore does not affect your personal data files (such as
Microsoft Word documents, browsing history, drawings, favourites, or
email) so you won't lose changes made to these files.
Disk Clean Up
Disk Cleanup Utility can easily determine which files on a hard drive
may no longer be needed and delete those files.
• Temporary Internet Files
• Temporary Application Files
In addition to freeing up potentially significant amounts of hard drive
space, using Disk Cleanup on a regular basis can significantly
improve system performance
File Compression
This utility is used to reduce the size of a file and can be used to
free up more room on backing storage.
Standard File Format for Graphics
Standard file formats are created to allow data to be recognised by
different computer systems.
For example, file created adobe Photoshop could be opened by
other programs.
• GIF
• JPEG
• TIFF
Will go into files formats in more detail under multimedia unit.
Application Software
A software program running on top of the operating system
(Windows, Mac) that has been created to perform a specific
task for a user.
Examples include:
• Word processing - Word/Word Perfect
• Spreadsheets - Excel or Lotus 123
• Graphic Packages – Photoshop, Paintshop Pro, Corel Draw
Application Requirements (Lets think about)
Before you purchase any application software you must
consider:
• Operating Systems
• RAM
• Processor Speed
• Hard Disk Space
• Peripherals Required (graphics cards or sound cards)
Operating System
Check to make sure the application software is compatible
with the OS currently in use.
Windows 98
Windows 2000
Windows XP
Mac OS 9
Mac OS 10
Microsoft Windows 2000
or Windows XP or later
operating system
RAM
Software will specify a minimum RAM requirement.
128 MB of RAM or above recommended.
Processor
Personal computer with an Intel Pentium 3 or equivalent
processor recommended
MHz required
Hard Disk
Consider the storage requirements of your software.
400 MB of available hard disk space
Hard Disk usage will vary depending on configuration,
custom installation choices may require more or less hard
disk space.
Peripherals
Super VGA(video graphic adaptor) (800 * 600) or higher
resolution monitor.
Types of Viruses
Viruses can be classed by three main types:
 File Virus – attach to files
 Boot sector virus – attach to boot sector of system
 Macro Virus – fairly common and causes the least damage.
(Inserting unwanted word on document)
File Virus
File viruses attach themselves to other software. When the software is run, the
virus first loads itself into memory so that in can further infect other files or begin
damaging the computer.
Most viruses fall into this category.
Boot Sector Virus
These viruses infect floppy and hard drives. The virus program will load first,
before the operating system
They used to infect a computer's start-up (Bootstrap loader) program so that the
virus would become active as soon as the computer started up.
Boot Sector Viruses are an older type of virus and not so common.
Macro Virus
Macro Viruses use commands (macros) embedded in other software
to infect and spread to other files viewed by that software. E.g. Word
and Excel have macros and macro viruses can spread by exploiting
these commands.
Hackers exploit the macro by creating a destructive macro within a
document. When the document open the macro will run and copy
itself to other documents.
http://youtube.com/watch?v=sxal31zIKdE
Techniques Viruses use to disrupt a system
Viruses act differently according to the way they were programmed.
Technique
Course of Action
Replication
Creates copies of itself into other executable files.
Each time an infected program is ran it reproduces
itself.
Camouflage
Disguises itself to avoid detection from anti-virus
software. Does this by adding fake instructions to the
code. Appear has harmless program.
Watching
Virus lies in wait or watch for a particular action
(specific key action or a date). Meantime, it replicates.
Delivery
Erases files, changing the file index, randomly
changing numbers in a spreadsheet, introducing loops
to slow system down. Spread by a network.
Other Infections
 Worm
 Trojan Horse
Worm
Worm spread from computer to computer (emails), but unlike
a virus, it has the ability to travel without any help from a host
program.
How it works
• Replicates itself on the system
• Uses a network (email)
• Not noticeable until it consumes the memory which slows for
the computer system
• Can flood a network with useless traffic which overwhelms
the network capabilities.
Trojan Horse
Harmful code is contained inside another code which can appear
harmless. Software (Malware) that appear to be doing one thing but
actually doing another task.
malicious and
software,
Trojan horse will do damage once installed or run on your computer.
Can get control and do its chosen form of damage
• Erasing or overwriting data on a computer
• Allowing remote access to the victim's computer. This is called a RAT
(remote access trojan)
• Spying on the user of a computer and covertly reporting data like
browsing habits to other people (see the article on spyware)
Celebrated case, a Trojan horse was a program that was supposed to
find and destroy computer viruses.
Some Trojans are designed to be more annoying than
malicious (like changing your desktop, adding silly active
desktop icons) or they can cause serious damage by deleting
files and destroying information on your system.
Trojans can also create a backdoor on your computer that
gives malicious users access to your system, allowing
confidential or personal information to be compromised.
Anti-Virus Techniques
There are techniques used by anti-virus software to detect a
virus include:
• Checksum
• Signature
• Heuristic
• Memory Monitoring
Check Sum
A simple measure for protecting the reliability of data.
How it Works
1. The anti-virus software scans an uninfected file and
calculates a checksum by adding up all the binary codes in
the file.
2. Whenever the file is to be used, the anti-virus software adds
up all the binary codes again and the checksum should match
the earlier checksum.
3. If the checksums don’t match then it may be that the file now
contains some virus code.
Virus Signature – How it Works
1. A known virus will contain a sequence of particular lines of code.
This sequence is known as its virus signature.
2. Anti-virus software keeps a database of known virus signatures and
refers to this when looking for viruses.
3. When it finds a macro, program or boot sector file with code
matching one of the known virus signatures then it has found a virus.
4. The virus signature database has to be updated regularly to make
this effective.
Heuristic
The term heuristics comes from a Greek word meaning ”to find”.
This technique involves using knowledge gained from what
existing viruses are like and how they act and using this past
knowledge when looking for new viruses. It will look for certain
“behaviour” in code e.g. Code triggered by date or time events,
code that searches for .exe files(programs), code that tries to
write to disk in an unusual way.
Heuristic detection makes intelligent guesses about what files
contain viruses.
Memory Monitoring
Anti-virus software that is loaded on start up.
• Monitors system
• Checks programs
• Checks files
Ever time opened, run
written to
• Checks boot files
• Checks disks
Disadvantage
Can cause delay in program loading and execution.
• Heuristic detection
•
Use of checksum
•
Searching for virus signature
•
Heuristic detection
•
Memory resident monitoring
• Memory resident
monitoring
This type of anti-virus software is
loaded into RAM on start up and
remains in operation constantly for as
long as the computer is left on.
•
Use of checksum
•
Searching for virus signature
•
Heuristic detection
•
Memory resident monitoring
It monitors all computer activity and checks programs for infection
when they are about to run.
It checks all programs and files being loaded, modified, copied or
decompressed to look for suspicious signs or activity.
This slows down system performance but can be very effective
at preventing the spread of viruses.
There are many standard file formats for graphic files. Each has
its own advantages and disadvantages and users should choose
formats carefully depending on the purpose for the graphic file.
Compression
Graphics files, particularly bit-mapped graphics, can generate
very large file sizes.
It is possible to analyse the data in the file and cut down on the
data which needs to be stored. This is known as compression.
Compression saves disk space but affects system performance as
saving and loading takes longer due to the extra processing
involved.
Lossless Compression
This technique manages to cut down on the amount of data
which needs to be stored but does not actually lose any of the
data. This means that the quality of the image is not affected.
Lossy Compression
This technique cuts down on the amount of data which needs to
be stored by discarding some of the data. This means that the
quality of the image is affected.
jpeg
•
jpeg
•
gif
•
TIFF
(Joint Picture Experts Group)
JPEG is designed for compressing either full-colour or grey-scale
It works well on
images of natural, real-world scenes.
photographs, naturalistic artwork, and similar material; not so well
on lettering, simple cartoons, or line drawings
It allows you to save graphics using 24 bit depth allowing 16
million colours.
It uses lossy compression and the user can decide between quality
and file size depending on the intended use.
gif
•
jpeg
•
gif
•
TIFF
(graphics interchange format)
GIF is normally used for diagrams, buttons, etc. which have a small
number of colours. It can also be used for simple animations.
It only allows you to save graphics using 8 bit depth allowing 256
colours.
It uses lossless compression and so retains quality but it cannot
achieve as big a reduction in file size as jpeg can.
TIFF
•
jpeg
•
gif
•
TIFF
(Tagged Image File Format)
TIFF is is an industry standard file format developed for the
purpose of storing high-resolution bit-mapped, grey-scale, and
colour images.
It allows you to save graphics using up to 32 bit depth allowing 4
thousand million colours.
It can use either lossy or lossless or no compression and is often
used with lossless or no compression when file quality is to be
maintained. This, of course, leads to large file sizes.
When choosing software it is important to examine the
system requirements to make sure that the software will run
on the hardware.
System requirements will typically include details on:
Memory
i.e. how much RAM is required for the software.
Storage Requirements
i.e. how much Hard Disk space is required for the software.
OS compatibility
i.e. which operating system it requires.
Select suitable software to support the following tasks:
Producing a multimedia catalogue
Setting up a LAN in a school
Developing a school website
Describe how the software will help with the task and include the
system requirements for each piece of software. (memory, storage
requirements and OS compatibility.)
Select suitable hardware, including peripherals, to support
the following tasks:
Producing a multimedia catalogue
Setting up a LAN in a school
Developing a school website
Describe how each piece of hardware will help with the task.