Int 2 Computer Software Notes

Operating Systems

Int 2 Computer Systems - Comp Software Information Sheet 5.4.1

Produced by P W Shadbolt Queensferry High School 2004

When you turn on a PC or Mac the electricity starts-up a

program (Boot File) based in a ROM chip which searches the

attached storage devices (usually the Floppy Disc Drive, then

the CD-ROM drive and then the Hard disc drive) for a program

called the Operating System., which it then loads into RAM

memory. The Operating System is a suite of programs that controls the hardware

and software running on the computer, allowing the user to communicate with

application programs and peripheral devices. Whether you load or save a file,

access the internet, print a hard copy or just type on the keyboard, the operating system is involved

working in the background. These programs remain in RAM until you turn your computer off.

STANDARD FUNCTIONS

An easy way of thinking what an operating system does is to think about the tasks that can be done on the

desktop of your computer. These are all tasks carried out by the operating system.

Operating systems have a number of Standard functions including

Memory management -

Controls where programs and data are stored in the RAM. It allocates suitable memory

locations to programs and data and makes sure that they don’t get mixed up.

File Management -

The operating system manages all the files that are located on backing storage. It is

responsible for

• Deleting, copying, creating and re-naming Files

• Keeping the physical information as to where files are stored.

• Formatting and Cataloging Discs

• Loading and Saving to/from Disc

• Ensures data is sent to the correct program

• Controlling access to files (read and write privileges)

Input / Output -

Reads information from the mouse and keyboard and reacts accordingly. Sends information

to the correct printer.

Error Reporting -

Sends messages to the user if there is a problem e.g. “out of memory”

Interpreting user’s commands -

This is the connection between the user and the computer. It makes sure that the

commands are valid and then translates them into instructions that the computer system can

follow. We call this the Human Computer Interface (HCI).

There are two main types of HCI

• WIMP interfaces such as Windows 95 and the Mac-OS

• Command Driven interfaces such as Unix and the Acorn MOS

If a computer system is to be user-friendly it must have an easy to use interface, on the other hand it must

be fast and flexible for the advanced user.

• Command Driven Interface

This is when all the functions of the package (Word processor, Database, etc.) are controlled by

commands e.g. PRINT, SCREEN, and SAVE etc. This is not a very suitable environment for non-experts

but means that an expert user can move quickly and easily to the point they want without having to take

time going through numerous menus. VIEW is an example of a command driven word processor.

Operating Systems



• WIMP (Windows, Icons, Menu and Pointer)

This environment is said to be the most "user friendly". This means that beginners can learn how to use

the system faster than other types of environment. The pull-down menus allows functions to be easily

available and have the advantage over menu-driven environments of not passing you from one menu to

another because all menus are available at all times. While having this ease of use for beginners the

WIMP environment also allows expert users to use command keys to access functions quickly. Some

micros even give you the opportunity to give a number of instructions with one command

WINDOW

This is an area of the screen that is used to display the document that the user is

currently working on. Most systems can have several windows open at the same

time, although only one is active at any time. You activate the window by using

the pointer.

ICONS

These are small graphics that are used to represent items such as files, printers, disk drives etc. They help

to make the operating system very user friendly.

MENU

This offers you a list of choices. The menu bar either at the top or bottom of the page will give you a list

of choices, which you can select from.

POINTER

The pointer is an icon that is moved around the screen by using the mouse or other input device. The

pointer is used to select from menus, select icons or make windows.

STANDARD OPERATING SYSTEMS

These are Operating Systems that are used by a number of different hardware manufacturers. The main

advantage for the hardware companies is that users feel at ease with an Operating System they have used

before; also there are many similar applications available due to the large market. There can be problems

with a file that has been created by the same application package but used with different operating

systems (e.g., Claris files created on the Mac are slightly different from those saved on the PC although

they can be accessed from the application)

ROM BASED OR DISC BASED

Most computer systems like the Macs and PCs have their Operating Systems on

disc (Disc Operating System). Some older systems like the BBC have their

Operating Systems on ROM inside the computer. The advantage of the ROM

based OS is that it works faster. This is because access to ROM is faster than access to disc or hard disc

drive. The disadvantage is that in order to upgrade or improve your Operating System you have to take the

computer apart to replace the chip. With the increase in access speed of hard disc drives there are very

few computers left that have ROM based operating systems.

There are four main types of operating systems in popular

use today: MS-DOS, Windows,

UNIX and MacOS. All four of these operating systems run

on personal computers.

Examples of operating systems

DOS is an old (early 1980s) command-line operating system

that requires the user to memorise and enter all commands

from a command prompt.

A DOS Window:

Operating Systems



Windows 3.1 (late 1980s) was Microsoft’s first

attempt at a Macintosh-like Graphical User Interface

(GUI); this interface allowed:

1. programs to be launched by double-clicking

icons with a mouse

2. files to be copied by drag and drop

3. much easier copy and paste.

Windows 95/98/ME/2000/NT/XP are a family of Microsoft 32-bit operating

systems. At the time of this writing these operating systems dominate the market and

are to be found on most people’s personal computers. Microsoft has come a long way

since Windows 3.1 and Windows has become much more powerful and stable.

OS2 began as a joint venture between

IBM and Microsoft. IBM finished and

marketed this operating system. It is not

used extensively today.

UNIX was originally a command-line based operating system like DOS (although

it predates DOS by more than a decade). However, UNIX now

incorporates all of the features of a modern GUI and more.

UNIX is most popular for companies and large institutions,

particularly for multiuser environments.

Linux is a UNIX-like operating system for personal

computers. Its primary distinguishing feature is that its source

code (basically, the text of the program) is freely distributed.

A worldwide community of users work to improve Linux.

MacOS X is the current operating system for Apple Macintosh

computers. Throughout the 1990s the operation systems for the Mac

were quite similar to Microsoft Windows. However, in MacOSX

Apple has decided to base their operating system on UNIX.

Applications



Application programs

A Computer Application is a computer program that has been designed to help people with a particular

task. Different applications help with different tasks. The one that is used will depend on the type of task

that the user wishes to perform. Application packages have been designed to:

PROCESS TEXT

This type of package can store and process documents that are text based.

These packages allow the user to enter, store and retrieve text documents

and to perform a wide range of operations on the text. For example,

deleting, inserting, spell checking and using search and replace. Text

processing packages also allow the user to change the style, font and format

of the text. The best example of a text processing package is word

processing packages. Text processors would be used to produce letters, reports,

PROCESS NUMBERS

This type of application is designed to enable the user to enter, store and process

numerical data. A spreadsheet package is an example of a number processing

package. The working area of a spreadsheet has been divided into rows and

columns that form the cells into which the data is entered. Cells can contain text -

this is generally used for labels and headings, numbers on which the calculations are

carried out, and formulae – this defines the calculation to be carried out on the

numbers. Number processing applications would be used by accountants, bankers,

insurance companies etc. to perform statistical or financial calculations and to

process mathematical or scientific data.

PROCESS DATA

This type of application enables the user to store, manipulate and retrieve

collections of data. A database is rather like an electronic filing system/address

book that you can question. You can put in as much

information as you want and then ask it to sort the

information in different ways or search for specific

information. In a simple database the data is

organised into separate distinct files, each with their

own records and fields. In more complex databases

the files are linked together to enable the user to

perform complicated sorts and searches. Databases

are used in a wide range of business, commercial and Government organisations to deal with tasks such as

resource management, record keeping and stock control. For example, the Police use databases to keep

track of criminals and all the cars in the country. If they wanted to, the Police could give you a list of

people who all have the same make, model and colour of car as you in the country.

PROCESS GRAPHICS

There are 3 main graphics applications - drawing, painting and business graphics packages

Drawing

Drawing packages store instructions in order to draw shapes. A drawing package is

useful for designing; for example; a new kitchen or planning a new house extension

as drawing packages can be precise and can scale the drawing up or down, for

drawing outlines or for drawing shapes. It is called an object-orientated package,

which means that it is made up of a series of objects (lines, boxes, circles etc.),

which can be altered and moved around.

Applications



Painting

Painting packages store the drawings as pixels. This

is called a bit-mapped package as it draws by filling in

the pixels (little dots) on the screen. It is used as

though you were painting with pencils and rubber.

Painting packages are ideal for producing artistic

effects in drawings such as tone and shading. They

are good for freehand drawings and are suitable for

graphics work where artistic effects are an important

element, for example when drawing a poster or a book illustration. It is

much more creative than the drawing package. The painting and drawing

packages can be easily mixed up. An easy way to remember the difference is that the painting package has

a rubber and a spray gun capability.

Business Graphics

Business graphics applications turn numbers and statistics into graphical form. They

are often included in spreadsheet packages and are useful for business reports,

presentations, sales figures and exam results.

COMMUNICATIONS SOFTWARE

Communications software is used to:

• regulate the speed of the modem

• store and dial phone numbers

• establish connections on the phone system

• record and carry out logging in procedure.

During the transmission, the communications software:

• encodes data transmitted

• co-ordinates transmissions with other computers

• checks for errors in transmission.

Communications Software and The Internet

Many complex communication tasks must be completed in order to access the Internet. The Internet

Service Provider (ISP) supplies the software that provides and carries out these tasks. One of the tasks of

the ISP is to manage the user’s connection to the Internet.

The World Wide Web (WWW)

The WWW is accessed via a browser. A browser is a program that provides the

user with the tools to help them navigate through the pages of the WWW. A

good browser will provide the following features:

• somewhere to enter the address of the page being searched for

• a bookmark to allow the user to find useful pages quickly

• a home button that takes the user to their own home page

• back and forward buttons to take the user through the web pages that they have recently visited

• a method of saving useful data to disk.

MULTIMEDIA SOFTWARE

There are 2 categories of multimedia software. Authoring software and software that provides

multimedia-based information systems.

Authoring Software

Authoring software allows the user to develop projects or presentations, which combine the elements of:

• graphics (still and video)

• animation

• sound

• text

Applications



The user selects what elements they require from a range of files held on backing storage and combines

them into a presentation by setting up links between them. Authoring packages are script based whereas

the multimedia document is linked together using commands or icons.

Multimedia-based Information Systems

Multimedia-based Information Systems are commercially based packages that provide

information to the user. An example of a multimedia-based system is the encyclopedia Encarta.

INTEGRATED PACKAGE

Apple Works and Microsoft Works are examples of

integrated packages. These consist of a combination of

word processing, spreadsheet, database, graphics and

communications packages linked together. This makes it

easy to combine information from the different packages

and it is usually a great deal cheaper than buying the

packages individually, although not usually as powerful.

Characteristics of an Integrated Package

• Integrated packages make it easy to copy data between packages.

• Integrated packages reduce the need to enter data as the same data can be

used in a whole range of applications. For example, numbers in a spreadsheet

file can be transferred to a word processing or database file.

• Integrated packages have a common HCI. This means that similar menus, windows, commands

and icons are used in each of the applications. This makes it easy to switch between applications

and therefore reduces training costs and learning time.

• Integrated packages help the user to complete complex tasks as tasks cannot always be solved

using the feature in one application package, the user may have to use the facilities of more than

one application to complete the task.

• Integrated packages help to increase productivity because it is easy to switch between

applications and transfer data between them and users do not need to open and close several

packages to solve complex problems.

Limitations of an Integrated Package

• Applications within the package are not as powerful as stand alone or

dedicated packages. For example, the word processing package does not offer the same range of

functions as a dedicated word processing package.

Objects & Operations



General purpose packages (GPPs)

These are application packages that are in common use and may be supplied with desktop computer

systems. GPPs are widespread because the data objects contained in each package fall into the categories

of text, number, data and graphics; these are the most commonly used data type in the field of computing.

The following table lists some of the objects and operations used in each of the four main GPPs:

Each of the above packages its own native file format; this means the file format in which the package

would normally save data. For example:-

Microsoft Word normally saves data as a Word file although it could be saved as several other data types.

In some operating systems (e.g. Windows) the data type can be identified by the file extension; in the case

of a Word file this is .doc.

If the file is saved as plain text then the extension is .txt, if saved as RFT then it is .rtf. In this way you can

tell what type a file is by its name.

Standard file formats allow data to be transferred between different computer platforms and also between

different applications. A plain text file can be read by a word processor, a spreadsheet package and a

database. This makes it possible to export data from any one of these packages and import it into another.

Standard File Formats



Application Standards When application packages first became popular

one of the main problems was that manufacturers

made little effort to ensure that their files could

be read by software made by other manufacturers.

This was particularly true of word processors, where for example files

created in Word could not be used in

Wordperfect. Manufacturers made an attempt to

address this problem by including the

ability to save word-processed files

as plain text or ASCII. As all word

processors could now read a common

file format the situation improved.

However, it was soon realised that

saving a document as plain text did not include the formatting of the original document (font, bold, italic,

etc.). The next aim was to have a common file format that would include the formatting so that documents

created in one word processing package could be totally compatible with others. This led to the

development of rich text format (RFT), which is still in use today. RTF includes the formatting codes.

Many application packages can now save documents in foreign formats to aid the portability of files.

Sometimes these problems can cause frustration for users when they want to use another computer to load

a file. The problems that can occur are:

The backing storage drive is different from the media the file is saved on.

For example - the file is saved on a floppy that has been formatted for a Mac and the

disc drive will only read PC formatted discs.

Differing operating systems and the files won't be recognised. An error message from

the operating system will be given to the user.

For example - an AppleWorks file was saved on a computer with

MacOS 8 and you try to load it on a PC, which has Windows 95 as its operating system.

The PC will look for the filename to have a specific suffix e.g. cwk.

The computer does not have the appropriate application software.

For example, the file was created on Microsoft Word and the other computer only has

AppleWorks.

Using a different computer or ensuring that your media is formatted for

the correct standard or installing different operating system software

could resolve the first two problems.

The third problem is typical as each

application saves files in its own way

and other packages find it difficult to

read these files. However, standards

have been set which allow the user to

save data in a format, which can be read by other packages.

Standard file formats for text files are: RTF (Rich Text Format), ASCII and text

Standard File Formats



RTF

Rich Text Format (RTF) is a file format that lets you exchange text files

between different word processors in different operating systems.

ASCII

ASCII (American Standard Code for

Information Interchange) is the most common

format for text files in computers and on the

Internet.

There are even groups of sad individuals who spend great amounts of time and

effort creating complex pictures using ASCII code. A simple search on Google

returned more than 7000 sites dedicated to this art form.

Text

The term text file is often used as a synonym for ASCII file, a file in which characters are represented by

their ASCII codes

However, the disadvantage of saving files using these standards is that

special formatting created within the original file may be lost e.g.

different styles, fonts and sizes.

These different formats can usually

be chosen in the Save As.... menu

using the Format option in each

package.

Viruses



Viruses

Most programs are designed to be useful; some, like

viruses, are not! A computer virus is self-replicating

piece of computer code that can partially or fully attach

itself to files or applications, and can cause your

computer to do something you don’t want it to do. Virus

behaviour can range from annoying to destructive, but

even relatively benign viruses tend to cause harm.

Viruses enter your system via e-mail, downloads from the internet, infected

floppy disks, homemade CDs and ‘fun’ websites.

Currently the primary vehicle for transmission of

computer viruses is e-mail. Viruses arrive on a

computer as an attachment to an e-mail, which,

when opened by the user, sends further copies of

itself to everyone in the user’s address book. Clearly

such a means of replicating can be highly prolific. In the case of infected floppy

disks, the disk acts as a carrier spreading the virus into each machine when it is placed into the drive.

Homemade CDs spread viruses in a similar fashion when the original CD has been

infected during its compilation.

The popular use of programs such as Napster and Kazaa, which

allow users anywhere on the internet to share files on each

other’s hard drives, has led to concerns about this being used as

a means of spreading viruses. According to an article in the UK-

based IT site, The Register, 6% of all the music downloaded from KaZaa is virus-laden.

When a virus program is executed it tends to perform four actions:

1. replication: copies itself to other files, particularly to .com and .exe files and the boot sector record

2. camouflage: attempts to disguise itself to avoid detection from anti-virus software

3. event watching: whenever the virus runs it checks for certain events, e.g. a specific date, when the virus

will activate

4. delivery: this is the purpose of the virus or what it does. This may be a simple jumbling up of letters or

wiping an entire hard drive.

Signs of a virus

There are a number of tell-tale signs that can

indicate that your computer has been infected

with a virus. They include:

• displaying unwanted messages

• strange sounds or visual effects

• computer keeps rebooting unexpectedly

• a flood of unexpected e-mails.

A common misconception is that all types of

interfering programs are viruses. They aren’t.

Worms, Trojan horses and viruses are in a

broader category of what analysts call ‘malicious

code.’

Anti-Virus Techniques

INT 2 Computer Systems - Comp Software Infosheet 5.4.6

Produced by S Lambert for Drummond Community High School Computing Department 2004

Anti-Virus Software Detection Techniques

Anti-virus programs are used to detect and remove viruses. However, detection and removal of viruses are

often difficult. Anti-virus software is necessary to help locate viruses and destroy them. Norton Ant-

Virus and Virex are two common anti-virus software.

When dealing with these types of viruses as well as using anti-virus software, there are various ways of

either preventing viruses or making the virus infection less costly and painful.

Install anti-virus software from a well known, reputable company, Update it regularly, and use it.

New viruses come out every single day (see above).

In addition to scanning for viruses on a regular basis, install an 'on access'

scanner and configure it to start automatically each time you boot your

system. This will protect your system by checking for viruses each time

your computer accesses an executable file.

Virus scan any new programs or other files that may contain executable

code before you run or open them, no matter where they come from. There

have been cases of commercially distributed floppy disks and CD-ROMs

spreading virus infections.

Anti-virus programs aren't very good at detecting Trojan horse programs, so be extremely careful

about opening binary files and Word/Excel documents from unknown sources. This includes

posts in binary newsgroups, downloads from web/ftp sites that aren't well known or don't have a

good reputation, and executable files unexpectedly received as attachments to email or during an

on-line chat session.

Be extremely careful about accepting programs or other

files during on-line chat sessions. This is one of the

more common means that users end up with a virus or

trojan horse problems.

Do regular backups. Some viruses and trojan horse

programs will erase or corrupt files on your hard drive,

and a recent backup may be the only way to recover

your data.

Ideally, you should back up your entire system on a regular basis. If this

isn't practical, at least backup files that you can't afford to lose or that

would be difficult to replace: documents, bookmark files, address books,

important email, etc.

Int 2 Computer Software Notes

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