Data Transmission

Direction of transmission may be:

1. Simplex: in 1 direction only  e.g. pc to printer
2. Half duplex: in both direction but not at the same time e.g. phone conversation
3. Full duplex:  in both direction simultaneously e.g.  broadband connection

Method may be:

1. Serial: sent 1 bit at a time over a single wire (easy to implement, suitable for long distance, but slower
2. Parallel: sent several bits of data at a time.  (suitable for short distance, faster, but difficult to synchronize data)

Synchronization may be:

1. Asynchronous: data is transferred in an agreed bit pattern having start and stop bits at both ends.
2. Synchronous: is continuous stream of data. Both sender and receiver are synchronized with each other.

Fetch Execute Cycle

1. PC contains address of next instruction
2. Address is then copied to MAR
3. Contents of that address is copied to MDR
4. Contents copied from MDR to CIR
5. PC is updated
6. Instruction in CIR is decoded and executed

Program Errors

A SYNTAX ERROR is where a program statement doesn’t obey the rules of the programming language. E.g. missing comma or spelling mistake in keywords

A LOGICAL ERROR When a program is being run, if it doesn’t do what it should do there is a logic error. E.g. writing incorrect formula.

An EXECUTION or RUNTIME ERROR means an error occurred after the execution of program like some hardware failure or user enters a value which causes Division by Zero error

Health risks associated with increased use of computers

• RSI in wrists or fingers from prolonged typing or repeated clicking of mouse button
• Headaches/eyestrain/dry eye from staring at a monitor for long periods of time
• Backache/Strain from sitting in same position for a long time/using chair with no adjustment

Functions of Operating Systems

1. Provides user interface 
2. Input/output control   
3. Security
4. Handling interrupts
5. Spooling  
6. Memory management  
7. Processor management  
8. Utilities (e.g. Copy, save, delete, re-name, etc.)  
9. Maintain user accounts 
10. Load/run software 
11. Error reporting/handling 
12. Multitasking/multiuser/multi-access  
13. File management

Computer Ethics

– Set of principles / laws that regulates the use of computer technology.

 It covers:

– Intellectual property rights (e.g. copying of software)

– Privacy issues (e.g. accessing personal information)

– Impact of computers on society 

Functions of a web browser

Explain the function of a web browser.

• Displays webpage
• interprets HTML document
• interprets scripts e.g. java script
• provides services like bookmark, history
• identifies protocol like https, SSL

Identification of SSL

State how it is possible for a user to know that a website is secured by looking at the web address.

Solution:

Use of https


A padlock appears in bottom of browser


Use of https


Protocol ends in "s"

How SSL works?

Describe three of the stages a web browser goes through to detect whether a website is secure.

1. requests web server to identify itself/view the (SSL) certificate
2. receives a copy of the (SSL) certificate, sent from the webserver
3. checks if SSL certificate is authentic/trustworthy
4. sends signal back to webserver that the certificate is authentic/trustworthy
5. starts to transmit data once connection is established as secure
6.  if website is not secure browser will display an open padlock/warning message

Cookies

A COOKIE is a packet of information sent by a web server to a web browser. They are able to carry out user tracking and also maintain user’s preferences.

Proxy Server

PROXY SERVER:

• It acts as an intermediary between the user and a web server.
• Allowing the internet ‘traffic’ to be filtered; they can block access to a website if necessary.
• Speeds up access to information of webserver using cache.
• Keeps a list of undesirable websites and IP addresses

Encryption

Symmetric

Asymmetric

Encryption is used primarily to protect data in case it has been hacked. Whilst encryption won’t prevent hacking, it makes the data meaningless unless the recipient has the necessary decryption tools described below.

There are two types of encryption:

• symmetric (using private key only)  
• asymmetric (using private key and public key)

SSL

Secured Socket Layer:

• It is a protocol/certification that allows data to be sent and received securely over internet.
• When SSL is applied the HTTP protocol is changed to HTTPs and padlock sign appears making HTTP over secure.
• HTTPs is slower than HTTP but secure for private and confidential data.
• After applying SSL, an encrypted link is established between server and client.

Firewall

A Software or Hardware which filters the  data coming into a network and going out of the network, examining the ‘traffic’ between the user’s computer (or internal network) and a public network (e.g. the internet)

Wardriving

The act  of locating and using  wireless internet connections illegally without knowledge of victim

How to Avoid Wardriving:

• Enable Firewall
• Use Wire equivalent privacy encryption
• Use strong password

Hacking

Illegal access to a computer system is known as Hacking

How to Avoid Hacking:

• Enable Firewall
• Install Anti-hacking softwares
• Put Strong passwords

Virus

Viruses are programs that self-replicate (copy themselves) and are designed to disrupt computer systems.

How to avoid Viruses:

• Do not install programs from unknown sources,
• Avoid unknown emails
• Install Anti-virus
• Update Antivirus programs

Spyware/ Keylogger

It is a software on victim's computer which collects data from victim computer without his knowledge.

It monitors key presses on a user's computer and relays that information back to the sender of keylogger.

How to avoid Keylogger/Spyware:

• Carefully use keyboard
• Install Anti-spyware softwares
• Use mouse for passwords

Pharming

In pharming malicious code is installed on victim's computer or on server to misdirect victim user to a fraudulent website in order to steal his personal or financial information without his knowledge.

How to avoid pharming:

• Be careful while surfing websites
• Install Anti-pharming softwares

Phishing

In phishing a legitimate looking email is sent to user containing a link when user clicks that, user is directed to fraudulent website to obtain his financial or confidential information.

How to avoid phishing:

• Filters by ISP
• Careful while visiting websites or opening email
• Don’t click links for opening site (Type address of website)

RFID

RFID stands for Radio Frequency Identification  is a sensor which uses electromagnetic technology to track those tracks attached to some objects.
It can sense for about 20 feet.
It is used in library, healthcare, supermarkets and for livestock etc.

Digital Pen

A digital pen is an input device which reads handwriting or brush stroke of user from a paper and converts it into digital form.

Digital Camera

It captures images and stores them digitally in a storage place or can be displayed on the screen of the same camera or on any output device.

Pin Reader/Card Reader

It is used to read from cards like debit/credit cards.
It reads pin entered by user and then verify
It accepts and encrypts user's personal Identification Number

OMR Optical Marks Reader

It can recognize humanly marked options in exam papers, surveys etc.
It is helpful in automated checking
It can sense filled circles, however, it can not sense ticks and crosses etc.

MICR Magnetic Ink Character Reader

It is used to verify legitimacy of bank cheques.

It can sense special ink which is sensitive to magnetic field.

OCR Optical Character Reader

It is a scanner which contains a software to read and understand text from images, from paper, or from PDF on screen and convert that into editable text.
It is best if someone needs to change printed stuff. However,it only recognizes text, so, images and tables etc. won't be covered in scanning.

BCR Bar Code Reader/Price Scanner/POS Scanner

It reads BAR codes from product and converts them into numbers or letters. BAR codes work as a Primary field of the Product table once it is decoded for computer data of other field is shown by computer like name, price, manufacturing date, expiry etc. of product.

3D Scanner

A 3D Scanner is an object which reads a 3D object from a small distance based on it's size, shape and appearance (like color) and stores it's image as a 3D image.

It is used:

• to create real looking images
• to create animation in movies and in video games
• to create 3D model           

Image Scanner

Features	Uses	Advantages	Disadvantages
-Used to read from paper or object and store in computer -converts hard copy into digital	-to scan hard copy into computer -old photos and important docs can be scanned	-fast scanning as compared to typing -easy to store images in computer -easy to update stored a image	-scanned images have less quality than original -They take much disk space -they take a lot of space

Touch Screen

Features	Uses	Advantages	Disadvantages
A screen to enter commands More suitable for use with limited amount of option	-cell phones and PDA, public information system at airports, interactive whiteboard and MCQs.	-Very fast and easy to use -No training needed	-limited option available on screen -Expensive compared to other input devices -Screen can be dirty

Remote Control

Features	Uses	Advantages	Disadvantages
Used to control other devices using infra-red signals	-To control *Hi-Fi systems *Satellite systems *DVD/Blue Ray  players *Projectors	-devices can be operated from remote -Can operate devices in unsafe environment like demolishing buildings	-Infrared signals get blocked with an object.

Joystick

Features	Uses	Advantages	Disadvantages
-A pointing device It has handle to move pointer and buttons to select options	Popular for: *gamming to control objects *controlling industrial machinery *use in simulators	-Easier to control object -Very simple to get use to	-Difficult to enter text -Difficult to control cursor