Operating System

+ Operating System (OS) is essentially software running in the background of a computer system.+ It manages many of the basic functions such as

* Multitasking * Management of user accounts * Multiprogramming * File Utilities (e.g. copy, save, sort, delete) * Batch Processing * Processor Management * Error Handling * Memory Management * Real-time Processing * Input and Output Control * Interrupt handling routines * Security (manages log on, passwords)

+ One of the most common examples of an operating system is known as Windows, Linux, UNIX and Android+ When the computer is switched on, the initiating programs are loaded into memory from ROM chip.+ These programs make sure that hardware, processor, internal memory and BIOS are all functioning correctly, if no error is detected then OS is loaded into memory+ Household appliance such as cookers, microwave ovens and washing machines do not have operating system since they are designed to carry out single tasks

Interrupts and Buffers

Three Types of Touch screen Capacitive: Made up of many layers of glasses that act like a capacitor, this creates an electric field when touched on the particular co-ordinates of screen the particular co-ordinate is determined by on-board processor

Advantages Disadvantages+ Medium Cost Technology + Only allows the use of bare fingers, however + Good Screen Visibility even in Strong sun light special stylus are now being designed + Permits Multi Touch capability+ Screen is very Durable, needs major impact to break

Infra-Red (Heat and Optical)

Heat Optical

+ It uses glass as a screen material + Uses glass as a screen material + Need warm objects to carry out the operation + Uses an array of sensor (in the form of grid) + (e.g. fingers for input) (( The point of contact is determined which co –

- ordinates of particular grid is touched ))

Advantages

Both System allows multi touch capabilities Both Systems have good screen visibility and takes a major impact to break Optical System allows the use of bare fingers , gloved fingers or a stylus

Disadvantages

Relatively Expensive Technology Heat Sensitive system disallows the use of gloved fingers and stylus They have fair screen visibility in strong sunlight

Resistive + This is made up of upper layer of polyester and bottom layer of glass + When the top layer of polyester is touched the top and bottom layer completes a circuit, + Therefore Signals are sent which are interpreted by microprocessor , hence the calculations determine the Co-ordinates where the screen is touched

Advantages Disadvantages + Relatively inexpensive technology + Screen visibility is poor in strong sunlight + Allows the use of bare fingers, gloved fingers + Does not permit multi touch capability and special stylus + Screen Durability is fair , it is vulnerable to scratches

Memory and Data Storage

Joint Photographic Experts Group (jpeg)- The size of file is reduced when a photographic file undergoes file compression.- One of the file Formats used to reduce photographic file sizes is known as (jpeg)- This is example of lossy file compression- Once the image is objected to jpeg compression algorithm, a new file is formed and the original file can no longer be constructed- Jpeg reduce RAW BITMAP (file extension .TIF BMP) image by a factor of 5 and 15- TIFF BMP are the highest image quality because, unlike jpeg they are not in compressed format .- JPEG relies on certain properties of human eye , file compression take place without any real loss of quality and hence a person is unable to detect very slight differences (The human eye is only able to differentiate 10 million colors)

Lossless and Lossy File Compression

Lossless Compression : Lossless compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data. This is particularly important where the loss of data is disastrous for e.g. a spreadsheet file

Lossy File Compression : With this technique, file compression algorithm eliminates unnecessary bits of data as seen in MP3 and JPEG formats.It is not possible to get the original file back once it is compressed.This is chosen for files where removing certain bits do not detract quality

Memory and Storage

+ Primary Memory + Secondary Storage + Offline Storage

Primary Memory

Random Access Memory (RAM)

Following are the features of RAM+ It is volatile/temporary memory (the contents of memory are lost when power to RAM is switched off)+ Used to store data ,files, or part of operating system that is currently in use

* The larger the size of RAM the faster the computer will operate . By increasing the size of RAM, the number of times this access operation is carried out is reduced, making the computer run faster…

* RAM is much faster to read and write from other types of memory but its main drawback is volatility

Two Types of RAMDynamic RAMMost Computers nowadays use DRAMsEach Dynamic RAM chip consist of millions of Transistors and Capacitors * Capacitor: This hold bit of information (0 or 1)* Transistors: It acts like switch, allows a chip control circuity to read the capacitor or change its value

Disadvantage of this Dynamic RAM is that its capacitor need to be constantly refreshed otherwise it loses its value

Advantage of Dynamic RAM+ Much less expensive than SRAMs+ Consume less power than SRAMs+ Have higher storage capacity than SRAMs

Static RAM (SRAMs)+ A big difference between SRAMs and DRAMs that this type of memory does not need to be constantly refreshed+ Make use of flip flop which hold each bit of memory+ SRAMs are much faster than DRAMs when it comes to access data (access time for SRAM 25 nanosecond and DRAM for 60 nanosecond)+ SRAMs are used where absolute speed is essential.

Read Only Memory+ They are non-volatile/permanent memory (the contents of memory remains save even when the power to ROM is switched off) + ROM is used to store start up instructions when the computer is switched on (ROM use to store BIOS)+ Contents of ROM chip can only be read and they cannot be changed

Application where both RAM and ROM chips are used+ A remote controlled toy car has a circuitry which contains both RAM and ROM chip.+ Remote Control is a hand held device

Following are the functions which ROM performs* stores factory reset settings * stores start up routines* stores set routines for e.g. how the buttons on remote control directions

Following are the functions which RAM performs* User may wish to review programs in their own routines, these instructions will be stored in RAM chip* RAM chip will store instructions received from remote control

Secondary Storage

Hard Disk Drives (HDD)

+ Data is stored in a digital format on the magnetic surfaces of the disks or “platters”+ Hard disks have number of platters which spin at about 7000 times a second+ Data is stored on the surface in sectors and tracks. (a given sector stores fixed number of bytes)+ The drawback of hard disk is that they have very slow data access operation compared to RAM+ Many applications require read write heads to seek data for the correct blocks + The effect of “LATENCY” then become very important (latency is defined as the time it takes for specific block of data on a data track to rotate around to the read-write head)+ Users sometimes notice the effect of latency when the see the message “Not responding”

Solid State Drives

SSD has removed the issue of latency considerably They have no moving parts and data is retrieved at same rateCommon type of Solid state storage devices store data by controlling the movement of e-SSD uses NAND chips and data is stored as 0s and 1s in millions of tiny transistors.This effectively produces non- volatile rewritable memory

Different Types SSD which sometime uses

Electronically Erasable Programmable Read Only Memory (EEPROM)+ The main difference is the use of NOR chips rather than NAND+ This makes them faster in operation and hence they are more expensive than those that use NAND technology+ EEPROM allows data to be read or erased in single bytes at a time where as use of NAND only allows blocks of data to

be read of erased + EEPROMs are mainly used where certain applications need to access or erase data at a time Because of the cost implications majority of SSD drives uses NAND technology

The two types are usually distinguished by the terms FLASH (use NAND chip) and EEPROM (use NOR chip)

Main Benefits of SSD rather than HDD+ They are more reliable (no moving parts)+ They are considerably lighter (suitable for laptops)+ Low power Consumption (suitable for laptops)+ Data access is considerably faster than HDD (because there is no issue of latency)+ They run much cooler than HDDs (suitable for laptops)+ No moving parts thus they are very thin

Off-line StorageOff-line storage includes:• CD/DVD/DVD-RAM (optical storage systems) CDs and DVDs use a red Laser light to read and write data on the surface of the disk CDs and DVDs use a thin layer of metal alloy or light sensitive organic dye to store the data CDs and DVDs use a single, spiral track where data is stored in pits and bumps CDs and DVDs can be designated as R (write once only) whereas RW is (data can be erased and written many times)

How DVDs are different from CDs+ Main difference is the use of dual layering which increases the storage capacity+ Two individual recording layers are used+ Two layers are joined together with a transparent (polycarbonate) spacer+ A thin reflector is also sandwiched between the two layers+ Reading & writing of the second layer is done by a red laser which focus at a fraction of millimetre difference compared to the first layer

DVDs with single layers still come with greater capacity because pits size and track width are smallerThe shorter the wavelength of the laser light the greater the storage capacity of the medium

DVD-RAMUses a very different technology to CDs and DVDs+ Instead of spiral track, they use a number of concentric tasks+ concentric tracks allow simultaneous read and write operations+ numerous read and write operations (up to 100,000 times)+ Great longevity (30 years) + Ideal for archiving

Concentric tracks

Blu-ray disks (optical storage systems)

How are Blu-ray disks different from CDs and DVDs?+ A blue laser is used rather than red laser to carry out read and write operations (wavelength of blue light is 405 nm compared to 650 nm for red light)+ Using blue light means pits and bumps can be much smaller+ Blu-ray stores 5x time more data than normal DVD+ Using two sandwiched layers can cause BIREFRINGENCE (light is refracted back into two separate beams causing reading errors) blue-ray uses only one layer, thus disks don`t suffer from birefringence+ Blu-ray disks automatically come secure encryption system which prevents privacy and copyrights infringement

+ These optical storage media are used as back-up systems (for photos, music)+ CDs and DVDs are used to transfer files+ Manufactures often supply their products using CDs and DVDs+ CDs and DVDs do not have that much capacity so movies and games are often supplied using Blu-ray disk

Future of Optical Media + Both CD and DVDs are showing the signs of becoming obsolete because many computers now come only USB connector+ Memory Sticks/Flash Memory are being used widely for transferring the files instead of CDs and DVDs+ Use of “Cloud“ is increasing to store all their files so it can be access from anywhere in the world+ There is no need of CD and DVD players because LED and LCD TVs are coming with USB connector while SMART TVs stream movies “ON DEMAND” using a internet wireless connection • USB flash memory/memory sticks (SSD system)+ Known as pen drives+ Main advantage is that they are very small and lightweight device+ Pen drives are used for small backups of music and photos+ Expert system, often uses memory sticks such as DONGLE (dongle contains additional files needed to run the software)+ Without Dongle software does not work properly (therefore it prevents unauthorized use)

SD-XD cards (SSD system)+ Digital Cameras use XD (eXtreme Digital) and SD (Secure Digital) cards which is then used to transfer photos to PC+ They have much smaller size than USB sticks+ Each SD cards is made up of NAND chips hence they have no moving parts+ All solid state drives need to be treated with some care because the data can go corrupt if they are removed from a device while it was in operation

• Removable/external hard disk drives (magnetic storage systems). + They are essentially Hard Disk Drives and can be connected through USB port+ They are used for backing-up files or used as a mean of transferring files between computers

How to Estimate the size of a File+ Each character from the keyboard has a value of 1 byte Suppose we typed in the following message:

“Hey bro how are you ?”So here are the properties

+ Hey bro how are you ? has exactly the same number of characters as the size of a file has number of bytes.+ File size for photos, one pixel (Red, Green, Blue) for example, occupies 3 bytes of memory.+ Obviously there are other codes stored with the file which make its real size slightly different, but we aren’t concerned

in this section of the topic

The photograph was 424 by 256 pixels which confirms the file size of (424*256*3) 325 632 bytes (318 kilobytes).

Security and Ethics

Hacking

Hacking: The act of gaining illegal access to a computer systemPossible effect of security risk: + This can lead to identity theft or gaining personal information

+ Data can be deleted, changed or corrupted

How to Prevent this: + Firewalls + Use of strong ids and password + Use of anti-hacking softwareNote: Use of encryption won’t stop hacking it simply makes the data useless and the hacker is still able to change or corrupt the data

Difference between hacking and cracking

Hacking is breaking into a computer to steal personal data while cracking is to edit a program source code in software so that the code can be exploited or changed for a particular purpose

Hacking isn’t necessarily harmful whilst cracking is ALWAYS totally illegal and is potentially very damaging

Viruses

Viruses: Program that can replicate itself with the intention of corrupting the file or causing the computer to malfunction

Possible effect of security risk: + Can cause computer to crash, stop + Can delete files/data + Can corrupt files data

How to Prevent this: + Installing antivirus software + Don’t use software from unknown sources + Be careful when opening attachments from unknown senders

Note: Backing up the files won`t guard it from viruses, it will simply reinstall

Phishing Phishing: The creator sends a legitimate looking email and as soon as you click the email you are directed to bogus/fake website

Possible effect of security risk: + The creator can gain your personal data such as bank account numbers + This can lead to fraud or identity theft

How to Prevent this: + Many ISPs now filter out phishing emails + The user should always be cautious whenever opening attachments or giving personal

information to any website

Note: Many legitimate looking emails often uses the names of large companies to convince users that email is authentic

Pharming

Pharming: Malicious code installed on user hard drive or on the web server that redirect to bogus website Possible effect of security risk: + The creator of malicious code can gain your personal data for e.g. bank account details

+ This can lead to fraud or identity theft

How to Prevent this: + Installing of anti-spyware software which remove pharming code from hard drives + User should be alert whenever he is being redirected to another website

Note: The user should look out for the clues such that it is https (secure website) or they must see a padlock sign next to URL

Wardriving

Wardriving: The act of using wireless internet connection illegally. It requires a portable device with wireless network card and an antenna to pick up the signals

Possible effect of security risk: It is possible to steal someone`s volume (data) by downloading large files It is possible to hack into wireless network and steal user`s password & personal details

How to Prevent this: + Use of wired equivalent privacy (WEP) encryption + Having more complex passwords before the internet can be accessed + Use of firewalls to prevent outside users from gaining access

Note: The user need to protect their password from other users, if any suspicious activity is seen password should be changed

Spyware/key-logging software

Spyware/Key-logging software: A type of software that gathers information by monitoring key presses on the user’s keyboard, the information is then sent back to the person who sent the software

Possible effect of security risk: + All data entered on user`s keyboard will be sent to the originator of the software + The software is able to install spyware, read cookie data and also change a user`s default web browser

How to Prevent this: + Use of anti-spyware software + User should be alert that their keyboard activity is being monitored + Use a mouse to select characters rather than using keyboard

Cookies

+ Cookies is a packet of information sent by a web server to web browser+ They are generated whenever a user visits a website+ Cookies are able to carry out user tracking and also maintain user`s preferences+ Cookies have now become an important part and many websites only allow the access when cookies are enabled often we see (Cookies are required to access this website)+ Cookies remember user`s previous buying habits and often this type of message is displayed (customers who bought items in your Recent History also bought XXXX)+ The information gathered by cookies forms an ANONYMOUS USER PROFILE and doesn’t contain personal information Loss of data and data corruption Recovery Methods or Safeguard Accidental loss of data + Use of backups in case data is lost (e.g. accidental deletion of data) + Save data on regular basis

+ Use of passwords and ids to restrict access for authorized users

Hardware fault + Use of backup in case data is lost through hardware fault (e.g. Crashing of hard disk drive) + Use of UPS to prevent power loss

+ Save data on regular basis + Use of parallel system as backup hardware

Software fault + Use of backups in case data is corrupted through the software fault (e.g. incompatible software + Save data on a regular basis in case software suddenly freezes installed on system)

Incorrect Computer Operation + Use of backup in case data is lost through wrong operation (e.g. incorrect procedure of shutdown + Correct training procedures so users should be aware of correct or removal of memory stick) operation of hardware

Firewalls

+ Firewall is a type of software that sits between computer and external network to filter out information.

Following are the tasks carried out by a firewall

+ It Examines the traffic between a computer and a public network (internet)+ It checks whether incoming and outgoing data meets the given criteria+ If the firewall does not meet the given criteria than the user is prompted/warned about the security risk+ A Criteria can be set to prevent undesirable websites (for e.g. firewall keeps a list of undesirable IP addresses)+ It helps to prevent viruses and hackers entering into someone`s computer

The software firewall often protects a single computer while a hardware firewall protects the whole server

The firewall can be a software or hardware interface located between a computer or internet connection and this firewall is often referred as a GATEWAY

Certain Circumstances where Firewall is not able to prevent harmful traffic

+ It cannot prevent individuals who use their own modems to bypass firewall+ Employees misconduct or carelessness cannot be controlled by firewall+ Users on stand-alone computer often disable their firewalls leaving their computer to harmful risk

All of these issues require management or personal control to make sure that firewall is allowed to do its job effectively

What is proxy server ?

It acts as an intermediary between user and web server

Functions carried out by a proxy server

+ Proxy server filters out internet traffic+ Proxy server can block access to particular website (similar reaction taken by firewall)+ Proxy server hides your IP from internet (this improves security) + Proxy server act as a firewall+ Proxy server uses CACHE which speed up access to information from a website

Security Protocols when using Internet

Secure Socket Layers (SSL)

+ This allows data to be send or received securely over Internet

+ SSL encrypts the data whenever a user visits a website so only the user and web server are able to make sense of what is being transmitted+ A user will notice a padlock or https ( ) in URL whenever SSL is being applied.

User`s web browser sends a message to web server to connect with the required website which secured by SSL

User`s web browser than request web server to identify itself

Web server respond by sending a copy of SSL certificate

The user on web browser authenticate the certificate which allows the communication to begin

Once the webserver receives the message of authentication SSL encrypted two-way data transfers begins

Transport Layer Security (TLS)+ It is a form of protocol which ensures the security and privacy of data more effectively than its predecessor SSL+ Whenever a website and user communicate over internet, TLS is designed to prevent third party hacking into this Communication

TLS is formed of two layers

Record Protocol: This part of communication can be used with or without encryptionHandshake Protocol: This allows the website and user to authenticate each other and make use of encryption algorithm

So what are the differences between SSL and TLS since they both perform the same job?

+ It is possible to extend TLS by adding new authentication method+ TLS separates handshaking process from record protocol which holds all data+ TLS make use of session caching

What is session caching ------ Not listed in Syllabus (learn the sentences as it is)+ Opening a TLS session requires a lot of computer time because complex encryption keys are being used+ The use session caching can avoid the need to utilize so much computer time by making a new or resuming the same connection

Encryption

+ Encryption is used to protect data by making it meaningless.+ Encryption won`t prevent hacking it simply makes the data useless + The recipient must have decryption key to decrypt the message to make it meaningful. Symmetric and Asymmetric Encryption are left and will be done sooner

Authentication Use of Passwords: + Usually a user id and password are required to login to many systems. + Both user id and passwords are checked against a secure file to ensure that it is the same person + If any of the thing is wrong than the access is denied

Biometric: + Fingerprint scans (Images of fingerprints are scanned and compared with the data bases if they match than access is allowed Accuracy is 1 in 500) + Retina Scans (This scans the unique pattern of blood vessel in retina which is very secure since no

one has been found with duplicate blood vessel Accuracy is 1 in 10 million) + Face Recognition (This scans a 2D image of a person and then check the following things for e.g. distance between the eyes, width of the nose, length of jaw line, shape of eye brows) + Voice Recognition + The user voice is detected and then converted into digital wave pattern)

+ This digital wave pattern is compared with the patterns stored in memory + If they match then the person has been correctly identified

Denial of Service Attacks

+ It is an attempt to prevent users from accessing part of a network. + It prevents a user from * Accessing their emails * Accessing websites * Accessing online services

+ One method of the attack is to flood the network with useless traffic (Obviously a server can only handle a finite number of requests, so it becomes over loaded when attacker sends thousands of requests and thus it is impossible to filter out user`s legitimate request)

+ Denial of Service Attack happens on a user`s email account too (Attackers sends out many spam messages, Obviously ISP allows a specific data quota for each user on their email account so user is unable to receive legitimate emails)

An individual user can guard against these attacks to some degree

+ Using up to date malware+ Setting up firewall to restrict traffic+ Applying e-mail filters to filter out spam emails or unwanted traffic

A user can be a victim of denial of service attacks, so here are the signs a user can look for + slow network performance + unavailability or inability to access some websites + large amount of spam reaching to user`s account

describe how the knowledge from 1.4.1, 1.4.2 and 1.4.3 can be applied to real-life scenarios including, for example, online banking, shopping see book section 8.8

Computer Ethics

+ Computer ethics are the set of principles set out to regulate the use of computer

Intellectual Property Rights: This covers for e.g. the copying of software without the permission of ownerPrivacy Issues: This covers for e.g. hacking or gaining illegal access to a computer systemEffect of Computer on Society: This covers factors such as job losses, social impact and so on

Plagiarism: This is when a person takes another person’s idea/work and claims it as their own. + It is fine to quote someone`s idea but some steps should be taken so that the originator of the idea should be known to others + Software now exists which actually can scan the texts and then look for examples of plagiarism by searching web pages

Free software, Freeware, Shareware

Free Software: A type of software where the user has the freedom to run, copy, change or adapt the software e.g. includes F-spot, Scribus, Abiword

A user is allowed to do the following things with the software+ Run the software for any legal purpose+ Study the source code and modify it as their needs+ Pass the software to their friends, family or colleagues

A user is not allowed to do the following things+ A user cannot add source code from another piece of software unless this is also described as free software+ A user cannot produce software which copies existing software+ A user cannot adapt the software in such a way that it violates the copyright rules+ A user may not use the source code which is offensive by third party

Freeware: Freeware are those software that can be downloaded from the internet with free of charge e.g. Includes Skype or Adobe + These type of software are subjected to terms and conditions hence a user is not allowed to study or modify its source code

Shareware: In this case a user is allowed to try out a software for a trial period

At the end of trial period, a request is prompted whether a user wants to buy the software (Very often, the trial version of the software is missing some of the features found in full version)

+ This type of software is protected by copyright laws hence a user is not allowed to use the source code + Permission need to be obtained before this software is copied or given to friends, family or colleagues

show understanding of the ethical issues raised by the spread of electronic communication and computer systems, including hacking, cracking and production of malware

copied from book(Note: ethical issues are raised as electronic communication continues to grow.Earlier in this chapter, issues such as hacking, viruses and other malware were considered. All of these put users at risk when using the internet or indeed any electronic device which transmits and receives data over a live link (e.g. mobilephones, tablets and other devices). Many users are aware that computers can undergo hacking or virus attack (and anyof the other security issues outlined earlier) but don’t seem to be aware that devices such as mobile phones are also vulnerable to attack by hackers and other people intent on causing harm to users of electronic devices.)