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

3. Applications software

2. Utility 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 CheckerA 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.

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.

malicious and software,

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

• Checks boot files

• Checks disks

Disadvantage

Can cause delay in program loading and execution.

Ever time opened, run written to

• Use of checksum

• Searching for virus signature

• Heuristic detection

• Memory resident monitoring

• Heuristic detection

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

• 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.

Lossless CompressionThis 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.

Compression saves disk space but affects system performance as saving and loading takes longer due to the extra processing involved.

Lossy CompressionThis 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.

(Joint Picture Experts Group)

It allows you to save graphics using 24 bit depth allowing 16 million colours.

jpeg

It uses lossy compression and the user can decide between quality and file size depending on the intended use.

• jpeg

• gif

• TIFF

JPEG is designed for compressing either full-colour or grey-scale images of natural, real-world scenes. It works well on photographs, naturalistic artwork, and similar material; not so well on lettering, simple cartoons, or line drawings

(graphics interchange format)

It only allows you to save graphics using 8 bit depth allowing 256 colours.

gif

It uses lossless compression and so retains quality but it cannot achieve as big a reduction in file size as jpeg can.

• jpeg

• gif

• TIFF

GIF is normally used for diagrams, buttons, etc. which have a small number of colours. It can also be used for simple animations.

(Tagged Image File Format)

It allows you to save graphics using up to 32 bit depth allowing 4 thousand million colours.

TIFF

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.

• jpeg

• gif

• TIFF

TIFF is is an industry standard file format developed for the purpose of storing high-resolution bit-mapped, grey-scale, and colour images.

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:

Storage Requirements

Memory

OS compatibility

i.e. how much RAM is required for the software.

i.e. how much Hard Disk space is required for the software.

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.