Monday, August 8, 2011

Quiz 9 - Computer Security and Safety, Ethics, and Privacy

1. Define the term, computer security risks, and briefly describe the types
of cybercrime perpetrators: hacker, cracker, script kiddie, corporate spy,
unethical employee, cyberextortionist, and cyberterrorist.

Computer security is a branch of computer technology known as Information Security as applied to computers and networks. The objective of computer security includes protection of information and property from theft, corruption, or natural disaster, while allowing the information and property to remain accessible and productive to its intended users. 
    Cybercrime Perpetrators
>Hacker refers to a computer programmer who is able to create usable computer programs where none previously existed. 
>Cracker is a variation of hacker , with the analogy equal to a safe cracker. Some individuals use the term cracker in an attempt to differentiate from the honorable computer programmer definition of hacker.
>Script kiddy is an individual who executes computer scripts and programs written by others. Their motive is to hack a computer by using someone else’s software. Examples include password decryption programs and automated access utilities. 
>Corporate Spy have excellent computer and networking skills and are hired to break into a specific computer and steal its proprietary data and information.
>Unethical employee break into their employers' computer for a variety of reasons. Some simply want to exploit security weakness.
>Cyberextortionist is someone who uses e-mail as a vehicle for extortion. These perpetrator s send an organization a threatening e-mail message indicating they will expose confidential information, exploit a security flaw, or launch an attack that will compromise the organization s network - if they are not paid of a sum of money.
>Cyber-terrorist a programmer who breaks into computer systems in order to steal or change or destroy information as a form of cyber-terrorism

2. Describe various types of Internet and network attacks (computer viruses,
worms, Trojan horses, rootkits, botnets, denial of service attacks, back
doors, and spoofing), and identify ways to safeguard against these attacks,
including firewalls, intrusion detection software, and honeypots.

A computer virus is a potentially damaging program that affects, or infects, a computer negatively by altering the way the computer works without the user's knowledge or permission. A worm is a program that copies itself repeatedly, using up resources and possibly shutting down the computer or network. A Trojan horse is a program that hides within or looks like a legitimate program. A root kit is a program that hides in a computer and allows someone from a remote location to take full control of the computer. To take precautions against this malware, do not start a computer with removable media in the drives or ports. Never open an e-mail attachment unless you are expecting the attachment and it is from a trusted source. Disable macros in documents that are not from a trusted source. Install an antivirus program and a personal firewall. Stay informed about any new virus alert or virus hoax. To defend against a botnet, a denial of service attack, improper use of a back door, and spoofing, users can install a firewall, install intrusion detection software, and set up a honeypot.
3. Discuss techniques to prevent unauthorized computer access and use


Unauthorized access is the use of a computer or network without permission. Unauthorized use is the use of a computer or its data for unapproved or illegal activities. Organizations can take measures such as implementing a written acceptable use policy (AUP), a firewall, intrusion detection software, an access control, and an audit trail. Access controls include a user name and password or passphrase, a CAPTCHA, a possessed object, and a biometric device.
4. Identify safeguards against hardware theft and vandalism


Hardware theft is the act of stealing computer equipment. Hardware vandalism is the act of defacing or destroying computer equipment. The best preventive measures against hardware theft and vandalism are common sense and a constant awareness of the risk. Physical devices and practical security measures, such as locked doors and windows, can help protect equipment. Passwords, possessed objects, and biometrics can reduce the risk of theft or render a computer useless if it is stolen.
5. Explain the ways software manufacturers protect against software piracy.


Software piracy is the unauthorized and illegal duplication of copyrighted software. To protect themselves from software piracy, manufacturers issue a license agreement and require product activation.
6. Discuss how encryption works, and explain why it is necessary


Encryption prevents information theft and unauthorized access by converting readable data into unreadable characters. To read the data, a recipient must decrypt, or decipher, it into a readable form. An encryption algorithm, or cypher, converts readable plaintext into unreadable cipher text. Encryption is used to protect information on the Internet and networks.


7. Discuss the types of devices available that protect computers from
system failure

A system failure is the prolonged malfunction of a computer. A common cause of system failure is an electrical power variation such as noise, an undervoltage, or an overvoltage. A surge protector, also called a surge suppressor, uses special electrical components to smooth out minor noise, provide a stable current flow, and keep an overvoltage from reaching the computer and other electronic equipment. An uninterruptible power supply (UPS) contains surge protection circuits and one or more batteries that can provide power during a temporary loss of power.
8. Explain the options available for backing up computer resources.


A backup is a duplicate of a file, program, or disk that can be used to restore the file if the original is lost, damaged, or destroyed. Users can opt for a full backup or a selective backup. Some users implement a three-generation backup policy that preserves three copies of important files: the grandparent, the parent, and the child. Others use RAID or continuous backup. Most operating systems and backup devices include a backup program.
9. Identify risks and safeguards associated with wireless communications.


Wireless access poses additional security risks. Intruders connect to other wireless networks to gain free Internet access or an organization's confidential data. Some individuals intercept and monitor communications as they transmit. Others connect to a network through an unsecured wireless access point (WAP), sometimes using the techniques of war driving or war flying. Some safeguards include firewalls, reconfiguring the WAP, and ensuring equipment uses a wireless security standard, such as Wi-Fi Protected Access (WPA) and 802.11i.
10. Discuss ways to prevent health-related disorders and injuries due to

computer use.

A computer-related repetitive strain injury (RSI) can include tendonitis and carpal tunnel syndrome (CTS). Another health-related condition is eyestrain associated with computer vision syndrome (CVS). To prevent health-related disorders, take frequent breaks, use precautionary exercises and techniques, and use ergonomics when planning the workplace. Computer addiction occurs when the computer consumes someone's entire social life.
11. Recognize issues related to information accuracy, intellectual property

rights, codes of conduct, and green computing.

Computer ethics govern the use of computers and information systems. Issues in computer ethics include the responsibility for information accuracy and the intellectual property rights to which creators are entitled for their works. An IT (information technology) code of conduct helps determine whether a specific computer action is ethical or unethical. Green computing reduces the electricity and environmental waste while using a computer.
12. Discuss issues surrounding information privacy, including electronic

profiles, cookies, spyware and adware, spam, phishing, privacy laws, social
engineering, employee monitoring, and content filtering.

Information privacy is the right of individuals and companies to deny or restrict the collection and use of information about them. Issues surrounding information privacy include the following. An electronic profile combines data about an individual's Web use with data from public sources, which then is sold. A cookie is a file that a Web server stores on a computer to collect data about the user. Spyware is a program placed on a computer that secretly collects information about the user. Adware is a program that displays an online advertisement in a banner or pop-up window. Spam is an unsolicited e-mail message or newsgroup posting sent to many recipients or newsgroups at once. Phishing is a scam in which a perpetrator attempts to obtain personal or financial information. The concern about privacy has led to the enactment of many federal and state laws regarding the disclosure of data. As related to the use of computers, social engineering is defined as gaining unauthorized access or obtaining confidential information by taking advantage of the trusting human nature of some victims and the naivety of others. Employee monitoring uses computers to observe, record, and review an employee's computer use. Content filtering restricts access to certain materials on the Web.

Monday, August 1, 2011

Quiz 8 Database Management

1. Define the term, database, and explain how a database interacts with data and information.
     Database is a collection of data organized in a manner that allows access, retrieval, and use of that data.
   
    Database interacts with Data    
      >Collection of unprocessed items
      >Text
      >Numbers
      >Images
      >Audio
      >Video
   Information
      >Processed data
      >Organized
      >Meaningful
      >Useful
2. Describe file maintenance techniques (adding records, modifying records,deleting records) and validation techniques.

     >File Maintenance  refers to the procedures that keep data current.    
     >Adding Records users add new records to a file when they obtain new data Disc
     >Modifying Records users modify a record to correct inaccurate data or update old data
     >Deleting Records When a record no longer is needed, a user deletes it from a file
     >Validation Techniques compares data with a set of rules or values to find out if the data is correct  

  • Alphabetic/Numeric check
  • Range check
  • Consistency check
  • Completeness check
  • Check digit
  • Other checks
3. Discuss the terms character, field, record, and file

    >Characters numbers, letters, space, punctuation marks, or other symbols   
    >Field is a combination of one or more related characters
    >Record is a group of related fields
    >File is a collection of related records

4. Discuss the functions common to most database management systems:
data dictionary, file retrieval and maintenance, data security, and backup
and recovery.

  A data dictionary contains data about cache file in the database and cache field within those files. A DBMS offers several methods to retrieve and maintain data, such as query languages, query by example, forms, and report generators. A query language is consists of simple, English-like statements that allow users to specify the data to display, print, or store. A query by example (QBE) has a graphical user interface that assists users with retrieving data. A form is a window on the screen that provides areas for entering or modifying data. A report generator allows users to design a report on the screen, retrieve data into the report design, and display or print the report. Backup - is the copy of the database.A log is a listing of activities that change the contents of the database. 
Recovery Utility - uses the logs and/or backups to restore the database.
5. Differentiate between a file processing approach and the database
approach.

File processing approach - each department or area within an organization has its own set of data files.Two major weaknesses of file processing systems are redundant data and isolated data.
Database approach- many programs and users share the data in a database. The database approach reduces data redundancy, improves data integrity, shares data, permits easier access, and reduces development time.A database, however, can be more complex than a file processing system, requiring special training and more computer memory, storage, and processing power. Data in a database also can be more vulnerable than data in file processing system.

6. Describe characteristics of relational, object-oriented, and
multidimensional databases.

Relational database-stores data in tables that consists of rows and columns. Each row has a primary key and each column has a unique name.
 
Object-oriented database (OODB) - stores data in objects;often use an object query language to manipulate and retrieve data.

Multidimensional databas-stores data in dimensions;allows users to access and analyze any view of the database data and no standard query language exists.
7. Explain how to access Web databases.

A Web database links to a form on a Web page. To access data in a Web database, you fill on the form or enter search text on a Web page. A Web database usually resides on a database server, which is a computer that store and provides access to a database.
8. Define the term, computer security risks, and briefly describe the types
of cybercrime perpetrators: hacker, cracker, script kiddie, corporate spy,
unethical employee, cyberextortionist, and cyberterrorist.

Computer security is a branch of computer technology known as Information Security as applied to computers and networks. The objective of computer security includes protection of information and property from theft, corruption, or natural disaster, while allowing the information and property to remain accessible and productive to its intended users. 
 
Cybercrime Perpetrators

Hacker refers to a computer programmer who is able to create usable computer programs where none previously existed. 

Cracker is a variation of hacker , with the analogy equal to a safe cracker. Some individuals use the term cracker in an attempt to differentiate from the honorable computer programmer definition of hacker.

Script kiddy is an individual who executes computer scripts and programs written by others. Their motive is to hack a computer by using someone else’s software. Examples include password decryption programs and automated access utilities. Corporate Spy - have excellent computer and networking skills and are hired to break into a specific computer and steal its proprietary data and information.

Unethical employee - break into their employers' computer for a variety of reasons. Some simply want to exploit security weakness.
Cyberextortionist - is someone who uses e-mail as a vehicle for extortion. These perpetrator s send an organization a threatening e-mail message indicating they will expose confidential information, exploit a security flaw, or launch an attack that will compromise the organization s network - if they are not paid of a sum of money.

Cyber-terrorist - a programmer who breaks into computer systems in order to steal or change or destroy information as a form of cyber-terrorism

9. Identify database design guidelines and discuss the responsibilities of
database analysts and administrators.

Database Analysts and Database Administrators are responsible for managing and coordinating all database activities.

Database Analysts (DA) - focuses on the meaning and usage of data. The DA decides on the placement of fields, defines the relationships among data, and identifies user's access privilege.

Database Administrators (DBA) requires a more technical inside view of the data. The DBA creates and maintains the data dictionary, manages data security, monitors database performance, and checks backup and recovery procedures. 


10. Discuss techniques to prevent unauthorized computer access and use

Operating system and software patches and updates
There is no such thing as perfect software, often a software program may have several issues and could potentially have security vulnerabilities that can leave your computer open to attacks that compromise your computer and your data.
Software patches, updates, and drivers are made available, often for free, to consumers to help keep a software program and operating systems running properly and secure. If the program you're using does not have any method of checking for updates on its own it is up to you to verify the program is up-to-date. Often this can be done by visiting the web site of the developer who created the program. A listing of third-party companies and links to each of their pages can be found on our third-party support page.
  • How to update a Microsoft Windows computer.
Passwords
Make sure a password has been set on computer. Default passwords such as password, root, admin or no password will allow easy access to your computer or your Internet account.
  1. Change passwords often. It is recommended at least once every few months.
  2. Create a BIOS password.
  3. When creating a password, add numbers or other characters to the password to make it more difficult to guess; for example: 1mypassword23!.
  4. Do not use sticky notes around your computer to write down passwords. Instead use a password manager.
  • Complete information and links to information about computer passwords.
Get a hardware or software firewall
We highly recommend all computer users have a firewall solution. There are two ways a firewall can protect your computer and network.
  1. Hardware firewall - A hardware firewall is a hardware device that is connected to your network. Often many home users who have a home network use their network router as a firewall solution.
  2. Software firewall - A software firewall is a software program that you install on your computer that helps protect that computer from unauthorized incoming and outgoing data. Below is a listing of a few of the more widely used software firewall programs.
Agnitum Outpost Firewall
BlackICE PC Protection
Kerio Personal Firewall
Sygate Firewall
Tiny software Tiny Personal Firewall
Network Associates
Zone Labs Zone Alarm
Note: A software firewall is only going to protect the computer that has the firewall installed on it.
In addition to the above listed firewall software programs many of the antivirus scanners released today also include their own version of a firewall program. If you have an antivirus scanner that also has a firewall program you do not need to worry about getting one of the above programs or another third-party firewall program.
  • How to enable or disable the Microsoft Windows firewall.
Trojans, viruses, spyware, and other malware
Software Trojans, viruses, spyware, and other malware can not only damage or destroy your computer data Internet or even log all your keystrokes to capture sensitive data such as passwords and credit card information. but is also capable of monitoring your computer to learn more about your viewing habits on the
To help protect your computer from these threats we suggest installing a virus protection program as well as a spyware protection program.
  • What are the current available antivirus programs?
  • My web browser has been hijacked.
Know how to handle e-mails
Today, e-mail is one of the most popular features on the Internet. Being able to identify threats sent through e-mail can help keep your computer and your personal information safe. Below are some of the most common threats you may encounter while using e-mail.
  • Attachments - Never open or run e-mail attachments. Viruses, spyware, and other malware are commonly distributed through e-mails that have attachments. For example, an e-mail may want you to open an attachment of a funny video, when it's actually a virus.
  • Phishing - Phishing or an e-mail phish is an e-mail that appears to be from an official company (such as your bank) indicating you need to log onto the site to check your account settings. However, the e-mails are actually sites setup to steal confidential information such as your passwords, credit card information, social security information, etc. See the phishing definition for additional information about this term as well as examples of these e-mails.
Alternative browser
Before the release of Microsoft Windows XP SP2 and Internet Explorer 7.0, Microsoft Internet Explorer was notorious for security and spyware related issues. Although it has improved since then we still highly recommend considering an alternative browser such as Mozilla Firefox.
Run system scans to check for vulnerabilities
There are several sites on the Internet that allow users to check their computers for potential threats or issues their network or computer may have that can allow users unauthorized access to their computer. Below are a listing of recommend sites to try: 
Gibson Research Corporation - The Gibson Research Corporation, or GRC, is a great location to learn about network security as well as well as test your computer or network for vulnerabilities. 

Hacker Wacker - Another great site with computer security related information, help, and programs to help test your computer and network.

Friday, July 22, 2011

Quiz 7 Communications and Networks

1. Discuss the components required for successful communications.
 Sending device — initiates instruction to transmit data, instructions, or information
Communications device — connects the sending device to the communications channel
Communications channel media on which data, instructions, or information travel
Communications device — connects the communications channel to the receiving device
Receiving device — accepts transmission of data, instructions, or information

2. Identify various sending and receiving devices.
A sending device initiates the transmission of data, instructions, and information while a receiving device accepts the items transmitted. All types of computers and mobile devices serve as sending and receiving devices in a communications system. This includes mainframe computers, servers, desktop computers, notebook computers, Tablet PCs, smart phones, portable media players, and GPS receivers.

3. Describe uses of computer communications.
Communications technologies include the Internet, Web, e-mail, instant messaging, chat rooms, newsgroups, blogs, wikis, RSS, VoIP, FTP, Web folders, video conferencing, and fax machine or computer fax/modem. Users can send and receive wireless messages to and from smart phones, cell phones, handheld game consoles, and other personal mobile devices using text messaging, wireless instant messaging, picture messaging and video messaging. A wireless Internet access point lets people connect wirelessly to the Internet through a wireless Internet access point. A hot spot is a wireless network that provides Internet connections to mobile computers and devices. A cybercafé is a coffeehouse, restaurant, or other location that provides computers with Internet access. A global positioning system (GPS) analyzes signals sent by satellites to determine an earth-based receiver’s geographic location.

4. List advantages of using a network
>Speed
>Cost
>Security
>Centralized Software Management
>Resource Sharing
>Email
>Work group computing

5. Differentiate among client/server, peer-to-peer, and P2P networks.
 Client server
>One or more computers act as server (host) and other computers, or clients, access server 

  Peer-to-peer
>Simple network that connects fewer than 10 computers 
>Each computer, or peer, has equal capabilities 

P2P networks
>Sometimes called a file sharing network
>Enables users to connect to each other's hard disks and exchange files directly
 
 6. Describe the various network communications standards.
 Network standards defines:
  •  Way devices access the medium
  •  Speed on different types of networks
  •  Types of network technology (cable / wireless)
Protocols
  •  Rules on how devices communicate with each other
  •  Data format used
  •  Coding Scheme
  •  Error Handling
  •  Sequencing techniques etc.
  •  Hardware / Software Vendors try to meet these guidelines
- ANSI, IEEE
- Standardizing Organization

7. Explain the purpose of communications software.
Communication software is used to provide remote access to systems and is also    used to exchange messages in text, audio and video format for the purpose of communication. This software sends and receives data over telephone lines through modems. The communication software allows computers in different geographical regions to communicate with each other through terminal emulators, file transfer programs, chat and instant messaging programs.

8. Describe various types of lines for communications over the telephone network.
  • PSTN - Worldwide telephone system that handles voice-oriented telephone calls.
  • Dial-up line - Temporary connection using telephone line for communications.
  • Dedicated line - Always on connection between two communication devices.  
9. Describe commonly used communications devices.
Dial-up modem
  • A dial-up modem converts digital signals to analog signals and vice versa
  • Usually in the form of an adapter card
DSL Modem / ISDN Modem-Cable Modem
  • Send and receive digital data from DSL(Digital Subscriber Line) / ISDN
Cable Modem 
>Sends and receives data over cable television (CATV) network
>Much faster than dial-up modem or ISDN   
>Sometimes called a broadband modem
Wireless Modem  
>Allows access to the Web wireless from a notebook computer, a smart phone, or other mobile device. 

Hub or Switch  
>Device that provides central point for cables in network. 
Router 
>Connects computers and transmits data to correct destination on network. 

10. Discuss different ways to set up a home network.


11. Identify various physical and wireless transmission media.
   Physical transmission media     
>Twisted-pair cable is used for telephone systems and network cabling*Separately insulated wires are twisted together in a pair*Twisting reduce the noise (disturbances)

>Coaxial cable is often used for cable television wiring 
*Single Copper wire in center
*Woven or braided metal

Wednesday, July 20, 2011

Quiz 6 - Operating Systems and Utility Programs

1.Define system software and identify the two types of system software.
System software is computer software designed to operate the computer hardware and to provide a platform for running application software.

Two Types of Software System 
An operating system (OS) is a set of programs containing instructions that work together to coordinate all the activities among computer hardware resources.A utility program is a type of system software that allows a user to perform maintenance-type tasks

 2.Briefly describe various server operating systems: Windows Server, UNIX,Linux, Solaris, and NetWare.

Windows Server is a brand name for a group of server operating systems released by Microsoft Corporation. All are part of Microsoft Servers

Unix (officially trademarked as UNIX, sometimes also written as Unix) is a multitasking, multi-user computer operating system. The Unix operating system was first developed in assembly language, but by 1973 had been almost entirely recoded in C, greatly facilitating its further development and porting to other hardware.    

Linux can be installed on a wide variety of computer hardware, ranging from mobile phones, tablet computers, routers and video game consoles, to desktop computers, mainframes and supercomputers. Linux is a leading server operating system, and runs the 10 fastest supercomputers in the world. Typically Linux is packaged in a format known as a Linux distribution for desktop and server use. 
 
Solaris is a
Unix operating system originally developed by Sun Microsystems. It superseded their earlier SunOS in 1993. Oracle Solaris, as it is now known, has been owned by Oracle Corporation since Oracle's acquisition of Sun in January 2010. Solaris is known for its scalability, especially on SPARC systems, and for originating many innovative features such as DTrace, ZFS and Time Slider. Solaris is registered as compliant with the Single Unix Specification.

NetWare is a
network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, with network protocols based on the archetypal Xerox Network Systems stack.

 3.Summarize the features of several embedded operating systems: Windows Embedded CE, Windows Mobile, Palm OS, iPhone OS, BlackBerry, Google Android, Embedded Linux, and Symbian OS.

Windows Embedded CE
is optimized for devices that have minimal storage—a Windows CE kernel may run in under a megabyte of memory. Devices are often configured without disk storage, and may be configured as a “closed” system that does not allow for end-user extension (for instance, it can be burned into ROM). Windows CE conforms to the definition of a real-time operating system, with a deterministic interrupt latency. From version 3 and onward, the system supports 256 priority levels and uses priority inheritance for dealing with priority inversion. The fundamental unit of execution is the thread. This helps to simplify the interface and improve execution time.

Windows Mobile for Pocket PC have these standard features:

Palm OS Garnet has the following features:
  • Simple, single-tasking environment to allow launching of full screen applications with a basic, common GUI set
  • Monochrome or color screens with resolutions up to 480x320 pixel
  • Handwriting recognition input system called Graffiti 2
  • HotSync technology for data synchronization with desktop computers
  • Sound playback and record capabilities
  • Simple security model: Device can be locked by password, arbitrary application records can be made private
  • TCP/IP network access
  • Serial port/USB, infrared, Bluetooth and Wi-Fi connections
  • Expansion memory card support
  • Defined standard data format for personal information management applications to store calendar, address, task and note entries, accessible by third-party applications.

iPhone OS features the following:
Home screen
The home screen (rendered by "
SpringBoard") displays application icons and a dock at the bottom of the screen where users can pin their most frequently used apps. The home screen appears whenever the user switches on the device or presses the "Home" button (a physical button on the device). The screen has a status bar across the top to display data, such as time, battery level, and signal strength. The rest of the screen is devoted to the current application.
Folders
With iOS 4 came the introduction of a simple foldering system. When applications are in "wiggle mode", any two can be dragged on top of each other to create a folder, and from then on, any other 10 "apps" can be added to the folder using the same procedure (maximum folders can handle is 12 on iPhone and iPod touch and 20 on iPad). A title for the folder is automatically selected by the type of applications inside, but the name can also be edited by the user.

Notifications screen 

In the iOS 5 update, the notifications feature has been revamped. Notifications now collate in a window which can be dragged down from the top of the screen (in a similar fashion to the Android OS).

Included applications

The iOS home screen contains these default "apps". Some of these applications are hidden by default and accessed by the user through the Settings app or another method—for instance, Nike+iPod is activated through the Settings app. All of the utilities, such as voice memos, clock, calculator, and compass are in one folder called "Utilities" in 4.0. Many of the included applications are designed to share data (e.g., a phone number can be selected from an email and saved as a contact or dialed for a phone call).
The iPod touch retains the same applications that are present by default on the iPhone, with the exception of the Phone, Messages, Compass and Camera (prior to the 4th generation) apps. The "iPod" App present on the iPhone is split into two apps on the iPod Touch: Music, and Videos. The bottom row of applications is also used to delineate the iPod touch's main purposes: Music, Videos, Safari, and App Store (Dock Layout was changed in 3.1 Update). For the 4th Generation iPod touch, it includes FaceTime and Camera, and the dock layout had changed to Music, Mail, Safari, Video. As of iOS 5.0 (to be released to the public in fall 2011), "iMessage" will be available on all iOS devices running iOS 5.

 
Multitasking
Before iOS 4, multitasking was limited to a selection of the applications Apple included on the devices. Apple worried that running multiple third-party applications simultaneously would drain batteries too quickly. Starting with iOS 4, on 3rd-generation and newer iOS devices, multitasking is supported through seven background APIs:
  1. Background audio
  2. Voice over IP
  3. Background location
  4. Push notifications
  5. Local notifications
  6. Task finishing
  7. Fast app switching

Switching applications 

Double-pressing the home button activates the application switcher. A scrollable dock-like interface appears from the bottom, moving the contents of the screen up. Choosing an icon switches to an application. To the far left are icons which function as music controls, and a rotation lock. Holding the icons briefly makes them wiggle (similarly to the homescreen) and allows the user to quit the applications.

Game Center 

Game Center is an online multiplayer "social gaming network" released by Apple. It allows users to "invite friends to play a game, start a multiplayer game through matchmaking, track their achievements, and compare their high scores on a leader board."

BlackBerry OS is a proprietary mobile operating system, developed by Research In Motion for its BlackBerry line of smartphone handheld devices. The operating system provides multitasking and supports specialized input devices that have been adopted by RIM for use in its handhelds, particularly the trackwheel, trackball, and most recently, the trackpad and touchscreen. The BlackBerry platform is perhaps best known for its native support for corporate email, through MIDP 1.0 and, more recently, a subset of MIDP 2.0, which allows complete wireless activation and synchronization with Microsoft Exchange, Lotus Domino, or Novell GroupWise email, calendar, tasks, notes, and contacts, when used with BlackBerry Enterprise Server. The operating system also supports WAP 1.2. Updates to the operating system may be automatically available from wireless carriers that support the BlackBerry over the air software loading (OTASL) service.

Google Android features the following:

Handset layoutsThe platform is adaptable to larger, VGA, 2D graphics library, 3D graphics library based on OpenGL ES 2.0 specifications, and traditional smartphone layouts.
StorageSQLite, a lightweight relational database, is used for data storage purposes
ConnectivityAndroid supports connectivity technologies including GSM/EDGE, IDEN, CDMA, EV-DO, UMTS, Bluetooth, Wi-Fi (no connections through Proxy server and no Ad hoc wireless network), LTE, NFC and WiMAX.
MessagingSMS and MMS are available forms of messaging, including threaded text messaging and now Android Cloud To Device Messaging Framework(C2DM) is also a part of Android Push Messaging service.
Multiple language supportAndroid supports multiple human languages. The number of languages more than doubled for the platform 2.3 Gingerbread. Android lacks font rendering of several languages even after official announcements of added support (e.g. Hindi).
Web browserThe web browser available in Android is based on the open-source WebKit layout engine, coupled with Chrome's V8 JavaScript engine. The browser scores a 93/100 on the Acid3 Test.
Java supportWhile most Android applications are written in Java, there is no Java Virtual Machine in the platform and Java byte code is not executed. Java classes are compiled into Dalvik executables and run on Dalvik, a specialized virtual machine designed specifically for Android and optimized for battery-powered mobile devices with limited memory and CPU. J2ME support can be provided via third-party applications.
Media supportAndroid supports the following audio/video/still media formats: WebM, H.263, H.264 (in 3GP or MP4 container), MPEG-4 SP, AMR, AMR-WB (in 3GP container), AAC, HE-AAC (in MP4 or 3GP container), MP3, MIDI, Ogg Vorbis, FLAC, WAV, JPEG, PNG, GIF (though earlier versions do not support animated GIFs), BMP.
Streaming media supportRTP/RTSP streaming (3GPP PSS, ISMA), HTML progressive download (HTML5 <video> tag). Adobe Flash Streaming (RTMP) and HTTP Dynamic Streaming are supported by the Flash plugin. Apple HTTP Live Streaming is supported by RealPlayer for Mobile, and by the operating system in Android 3.0 (Honeycomb). Microsoft Smooth Streaming is planned to be supported through the awaited port of Silverlight plugin to Android.
Additional hardware supportAndroid can use video/still cameras, touchscreens, GPS, accelerometers, gyroscopes, magnetometers, dedicated gaming controls, proximity and pressure sensors, thermometers, accelerated 2D bit blits (with hardware orientation, scaling, pixel format conversion) and accelerated 3D graphics.
Multi-touchAndroid has native support for multi-touch which was initially made available in handsets such as the HTC Hero. The feature was originally disabled at the kernel level (possibly to avoid infringing Apple's patents on touch-screen technology at the time). Google has since released an update for the Nexus One and the Motorola Droid which enables multi-touch natively.
BluetoothSupports A2DP, AVRCP, sending files (OPP), accessing the phone book (PBAP), voice dialing and sending contacts between phones. Keyboard, mouse and joystick (HID) support is available through manufacturer customizations and third-party applications. Full HID support is planned for Android 3.0 (Honeycomb).
Video callingAndroid does not support native video calling, but some handsets have a customized version of the operating system that supports it, either via the UMTS network (like the Samsung Galaxy S) or over IP. Video calling through Google Talk is available in Android 2.3.4 and later.
MultitaskingMultitasking of applications is available.
Voice based featuresGoogle search through voice has been available since initial release. Voice actions for calling, texting, navigation, etc. are supported on Android 2.2 onwards.
TetheringAndroid supports tethering, which allows a phone to be used as a wireless/wired hotspot. Before Android 2.2 this was supported by third-party applications or manufacturer customizations.
Screen captureAndroid does not support screenshot capture as of 2011. This is supported by manufacturer and third-party customizations.