Higher Computing

Computer Software

What you need to know!• Description of the function of a bootstrap loader

• Description and exemplification of the main functions of a single user operating system: interpreting users commands, file management, memory management, input/output management, resource allocation, managing processes

• Definition of a utility program

• Description of utility programs (including virus checker, disk editor and defragmenter)

• Description of the standard file formats for graphics files: JPEG, GIF, TIFF

• Description of a suitable selection of software to support typical tasks including production of a multimedia catalogue, setting up a LAN in a school, development of a school website

• Description and exemplification of software compatibility issues (including memory and storage requirements, and OS compatibility)

• Classification of viruses by type of file infected: file virus, boot sector virus, macro virus

• Description of the following virus code actions: replication, camouflage, watching, delivery

• Distinction between a virus, a worm and a Trojan horse

• Description of anti-virus software detection techniques: use of checksum, searching for virus signature, heuristic detection and memory resident monitoring

Bootstrap Loader

• A bootstrap loader is a small but important piece of software which is held in ROM.

• As soon as you turn the computer on the bootstrap loader starts to run.

• It looks for the operating system, usually held on disk, and begins to load it into main memory.

Functions of an operating system• The operating system is a program that

controls the entire operation of the computer and any devices attached to it.

• The main functions include:– Interpreting user commands– Managing files– Input/Output– Memory management– Resource allocation– Managing processes

Interpreting User Commands

• The OS involves taking instructions or commands from the user, checking them, then passing them to the correct part of the OS to be carried out.

• In early OS these were typed commands.• In modern systems the OS will have to

check menu selections and mouse click commands.

Managing Files

• The file management organises and tracks files.– Maintaining a directory which keeps track of where

files are stored across the various types of devices.

– Providing a connection between the user’s logical view of the files and the actual physical locations of the files.

– Supports manipulation of the data in a file.

– Protecting file integrity by controlling access.

– Requesting transfers of data from I/O devices.

Input/Output

• The I/O performs the actual data transfer between peripherals and memory.– Control and timing to coordinate data flow.– Communicating with the processor by

accepting CPU commands about whether devices are ready to send/receive data.

– Data buffering to regulate the speed between processor and main memory.

– Detect errors such as mechanical or electrical failures

Memory Management

• This part of the OS organises the storage of data.– To load programs into memory so each

program has all the memory required.– Monitor the use of memory.– Free memory locations when data is no longer

needed.

Resource Allocation

• This refers to the process of allocating memory and CPU time to programs.

• Allocating memory is usually a matter of admitting processes to the memory if there is enough space or delaying until there is space available.

• In a single-program OS the only processes being run are those generated by either the OS or by the one program that is running.

Managing Processes• A process is a program that is being

executed plus all the resources that are associated with the program (buffers memory locations, data files etc.)– Allocates resources to the process such as

memory– Schedules CPU time– Maintains the integrity of the process– Terminates the process and restores all system

facilities so that they can be accessed by other processes.

Utility Programs

• Utility programs are software design to carry out a specific task related to the management or maintenance of a computer system.

• They are not part of the core operating system as the are not needed on a continuous basis.

• To need to be able to describe different utility programs.– Virus checker– Disk editor (disk clean up)– Recovery– Disk defragmenter– Printer drivers

Virus checker

• A virus is a rogue program written with the intention of causing damage to a computer system.

• Virus checking software should be able to detect a virus infection and remove it from a computer system.

• New viruses are constantly being written, so virus checking software allow the user to download updates from the internet.

Disk editor (disk clean up)

• A disk editor enables you to get rid of all sorts of unnecessary files that clutter up your system, some of which you might not know exist.

• These files include:– Temporary internet files– Temporary files used by applications– Offline web pages

Recovery

• This is used to restore files that have been corrupted.

• The utility normally has a wizard which will help locate an intact copy of your files from backup.

• This copy is then used to replace the corrupted files on your system.

Disk defragmenter

• Filing systems try to save files in contiguous blocks (next to each other).

• As files are deleted and changed, spaces appear throughout the disk.

• A disk defragmenter rearranges the files so that they are next to each other.

• This speeds up access time and frees up disk space.

Printer drivers• Printers can produce different styles and

typefaces.• Before the printer can produce these effects it

must have the correct code sent from the computer.

• Different printers use different codes to produce the same effect.

• Printer drivers are software that takes the codes used in the document and translates them into the appropriate code for the printer.

Standard File Formats

• In order for the OS to recognise the application used to save a file, File name extensions are used (usually three letters). E.g. GIF, JPG, TIF.

• Each type of application has its own set of standard file formats.

• Here are some examples:– JPEG– GIF– TIFF

JPEG(Joint Photographic Experts Group)

• JPEG is designed for either full colour or greyscale of natural scenes.

• JPEG uses 24 bits per pixel to store RGB colour images (16.8 million possible colours)

• Good for photographs / Poor at line drawings.• Lossy compression between 2:1 and 30:1• The amount of compression allows a trade-off

between file size and quality.

GIF (Graphics Interchange Format)

• GIF is used for compressing bit-map images so they can be transferred via the internet quickly.

• GIF images are limited to 256 colours (8Bit)• Good at Logo’s and line drawings which have large

blocks of the same data.• GIF allows interlaced images. ( a low quality

version can be displayed while the rest of the image is being transmitted.

• GIF supports transparency.• GIF uses lossless compression.

TIFF(Tagged Image File Format)

• TIFF is used for high resolution bit-map images.

• TIFF files are large and not used on web pages.

• TIFF files are uncompressed.• TIFF files are widely used in Photoshop,

Desktop Publishing and scanning. • TIFF are used when high quality images

are required.

Selection of software

• You are required to select appropriate software for the following tasks:– Production of a multimedia catalogue.– Setting up a Local Area Network in school.– Development of a school website.

Multimedia Catalogue• A multimedia catalogue is a database of products

containing a variety of media e.g. Sound, graphics and Video.

• The following software would be appropriate:• Multimedia authoring software, which ranges

from easy to learn packages like Hyperstudio, to major applications like Macromedia Director.

• A database which allows the inclusion of different multimedia elements.

Setting up a LAN in school

• Any modern operating system should be capable of peer-to-peer networking.

• If a client-server network is to be set up server software is required.

• Typical example of server software include Microsoft Windows Server and Mac OS X Server.

• In a school it is likely that computers in the same department will share the same platform.

• A database server may be required running software like Microsoft SQL Server.

Development of a school website

• There is a wide range of software that is capable of creating web pages for a school website.

• It may be advisable to select software capable of WYSIWYG page editing.

• The choice of software will depend on the expertise of the user and the complexity of the website to be created.

• Applications may range from the straightforward Microsoft Frontpage to the more complex Macromedia Dreamweaver.

Compatibility Issues

• Software which runs on a particular computer system is said to be compatible with that system.

• There are a number of issues that include:– Memory requirements– Storage requirements– OS compatibility

Memory Requirements

• RAM is used to hold the data while it is being processed.

• The technical guide for an application specifies the amount of RAM required for the application.

• If there is not enough RAM available then disk space may be used in its place. This is known as Virtual Memory and is around 1000 times slower than RAM.

Storage Requirements

• The storage requirements refer to the amount of backing storage needed to store the program to be installed.

• The technical guide will specify the amount of storage required for the application.

• Some applications require lots of backing storage so a range of installation option are available– Complete installation

– Customised installation

– Minimal installation

OS Compatibility• There are 3 main types of OS used in

desktops and laptops, Windows, Unix and Mac OS.

• Software is programmed to be compatible with a specific OS.

• Software companies supply more than one version of their product.

• Some programs are only compatible with a particular version of the OS e.g. Windows XP.

Viruses

• A Virus is a program which can destroy or cause damage to data stored on a computer system.

• Viruses can be classified by the type of files they infect.– Files– Boot Sector– Macro

Files Viruses

• File viruses are so called because they attach themselves to files.

• They either replace the code in the file or insert code into the file.

• The types of file they infect are have the extensions:.COM.EXE

Boot Sector Viruses

• Every disk drive contains a boot sector containing information about the format of the disk and a small program.

• By infecting the boot sector program the virus can guarantee it gets run.

• Once it has been run it waits until other disks are entered.

• Boot sector viruses are less common now that software is distributed on CD-ROM.

Macro Viruses

• A macro is and automated sequence of operations which can be recorded in a document.

• Programs like Word & Excel allow the user to make macros.

• A macro virus infects a document and causes a sequence of malicious instructions to be performed when the document is opened.

• Macro viruses cannot affect documents created by applications which do not support macros.

Virus Actions

• Viruses act differently according to how they are programmed.

• The action that viruses can carry out include:– Replication– Camouflage– Watching– Delivery

Replication

• The virus copies itself into other program files.

• Each time the program is run by the computer it reproduces itself.

• A worm can make copies of itself.

Camouflage

• Viruses us a variety of methods to camouflage their existence.

• One method is to create a false programming code mixed with good code.

• Each time the virus runs it changes the false code to avoid detection.

Watching

• A virus can lie watching for a particular action or date before it is activated.

• The longer the time before activation, the greater the number of computer systems which may get infected.

• A virus which watches for a date is called a time bomb.

• A virus which watches for an action is called a logic bomb.

Delivery

• The delivery of a virus is the method used in order to enter the computer system.

• Viruses spread in seconds over networks.

• Email is the main delivery method, along with file sharing and instant messaging.

• Viruses can also be delivered through any re-writable disk.

Distinction between a Virus, Worm and a Trojan horse.

• A Virus is a program which can destroy or cause damage to data stored on a computer system.

• A worm is a form of virus that makes copies of itself and spreads without being attached to a file.

• A Trojan Horse is disguised as another type of file, even pretending to be an antivirus program.

Antivirus Detection Techniques

• Antivirus detection techniques include:– Use of checksum– Searching for virus signature– Heuristic detection– Memory resident monitoring

Use of Checksum• A checksum is a value calculated for a given

set of data and is normally used to check that data has been transmitted correctly.

• The answer to the calculation is sent along with the data then recalculated and compared.

• This same process is carried out by antivirus software as a change in the code would also result in a different checksum being calculated.

Searching for Virus Signature• A virus signature is a characteristic

pattern or sequence that is known to be part of a virus.

• Antivirus software scans inside the code to look for recognised patterns.

• Some viruses have the ability to change their code on every infection so that a virus signature cannot be found.

Heuristic Detection• Heuristic detection uses general rules that

describe how viruses look and behave.

• It allows rules to be set up to detect new virus that haven’t been seen before.

• Many anti-virus programs allow the user to vary the sensitivity of the heuristic rules.

Memory Resident Monitoring

• Memory resident software loads into the computers memory as it is started up and stays until it is shut down.

• This is done in order to constantly check the computers memory for the presence of viruses.

• Memory resident monitoring can slow down the operation of the computer.

What you should now know!• Description of the function of a bootstrap loader

• Description and exemplification of the main functions of a single user operating system: interpreting users commands, file management, memory management, input/output management, resource allocation, managing processes

• Definition of a utility program

• Description of utility programs (including virus checker, disk editor and defragmenter)

• Description of the standard file formats for graphics files: JPEG, GIF, TIFF

• Description of a suitable selection of software to support typical tasks including production of a multimedia catalogue, setting up a LAN in a school, development of a school website

• Description and exemplification of software compatibility issues (including memory and storage requirements, and OS compatibility)

• Classification of viruses by type of file infected: file virus, boot sector virus, macro virus

• Description of the following virus code actions: replication, camouflage, watching, delivery

• Distinction between a virus, a worm and a Trojan horse

• Description of anti-virus software detection techniques: use of checksum, searching for virus signature, heuristic detection and memory resident monitoring