What is a computer?
Ports and expansion slots
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Ports and expansion slots. Various ports connect external devices to the system unit though cables. For example, there are serial ports that transmit one byte of data at a time. They are used mainly to connect devices such as a mouse and keyboard. Parallel ports transmit more than one byte of data at a time, and are therefore used to connect faster devices such as printers. SOFTWARE Software, otherwise known as a program, is a series of instructions that tells the computer what to do and how to do it. Categories of software There are two main categories of software. There are: System Software Application Software System Software System software consist all the programs including the operating system that control or maintain the operation of the computer and its devices. System software serves as an interface between the user, the application software and the computer’s hardware. Some of the functions that the system software performs include: Starting up the computer Loading Executing storing applications software (Office software’s) Type of system software Operating system Utility program Translators Operating System An operating system is a set of programs that co-ordinates all the activities among computer hardware devices. It provides a means for users to communicate with the computer and other software. When a user starts a computer, portions of the operating system load into memory from the computer’s hard disk. It remains in memory while the computer is on. Starting a Computer The process of starting or restarting a computer is called booting. The first thing a computer does when you turn on the power button is to check that it is working properly by following certain instructions held on a ROM chip known as the BIOS. Basic Input/output System (BIOS) is the program which starts up your computer and communicates between the devices in your computer. It will then look for an operating system (OS) to tell it what to do next. The operating system is loaded from the disk to the computer’s random access memory (RAM). When turning on a computer that has been powered off completely, you are performing a cold boot. A warm boot is the process of using the operating system to restart a computer. TYPES OF OPERATING SYSTEMS Multi User A multi-user operating system allows many different users to use the same computer at the same time. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Unix, Linux and Windows 2000, are examples of multi-user operating systems. Multiprocessing - An operating system capable of supporting and utilizing more than one computer processor. Examples of multiprocessing operating systems Linux, Unix and Windows 2000 Multitasking - An operating system that is capable of allowing multiple software processes to run at the same time. Examples of multitasking operating systems Microsoft's Windows and Apple's MacOS. MultiProgramming-the ability of a computer to execute two or more programs at the same time using one CPU or processor. Examples of Operating Systems MS-DOS (Microsoft Disk Operating System) LINUX
UNIX Mac OS X
Windows 7 Windows Vista Windows XP Windows 8 Functions of the operating system An operating system performs a number of basic functions that enable you and the application software to interact with the computer. These functions involve: Allocating System Resources The primary function of the operating system is to allocate, or assign the resources of the computer system. That is just as a police officer directs traffic, the OS decides what resources will currently be used and for how long. The resources include the CPU, main memory and the input and output devices such as disk, tape drives and printers. Memory Management During processing, items such as the operating system, application program instructions, data waiting to be processed and work space used for calculations, sorting and other temporary tasks are stored in main memory. It is the OS job to allocate, or assign each of these items to memory space in main memory. Data that has just been read into main memory from an input device or is waiting to be sent to an output device is stored in areas of maim memory called buffers. The OS assigns the location of the buffer in main memory and manages the data that is stored in them. INPUT AND OUTPUT MANAGEMENT At any given time, more than one device can be sending data to the computer. At the same time, the CPU could be ready to send data to an output device such as a terminal or printer or a storage device such as a disk. The OS is responsible for managing these input and output processes. The OS keeps track of disk read and write requests, stores these requests in buffers along with the associated data for write requests, and usually process them sequentially. Buffer refers to a temporary storage location that holds data during input output operations. They are used to compensate for the difference in processing speed for devices and the processor. E.G. A printer would be restricted to a specific user if the printer was going to be used with pre-printed forms, such as payroll checks. Monitoring system Performance Operating systems typically contain a performance monitor, which is a program that assesses and reports information about various system resources and devices. For example, you can monitor the CPU, disks, memory, and network usage, as well as the number of times a file is read or written, the information in these reports can help you identify problems with resources so you can attempt to resolve the problem. For example, if you computer is running extremely slow and you determine that the computer’s memory is utilized to its maximum, then you might consider installing additional memory. Administering Security Most multi-user operating systems allow each user to log on, which is the process of entering a user name and a password into the computer. This helps prevent unauthorized users from accessing those computer resources. Before you can use a computer that requires a log on procedure, you must enter your user name and password correctly. As you enter these items, a computer compares your entries with a list of authorized user name and passwords. If your entries match the user name and password kept of file, you are granted access; otherwise, you are denied access. System administrators also use these files to monitor computer usage. Some operating systems also allow you to assign passwords to files so that only authorized users can open them. Providing File and Storage Media Management Operating systems also contain a type of program called a file manager, which perform functions related to storage and file management. Some of the storage and file management functions performed by a file manager are: Formatting and copying disks Displaying a list of files on a storage medium Checking the amount of used or free disk space on the storage medium Copying, renaming, deleting, moving, and sorting files Utility programs - A program that performs a specific task related to the management of computer functions, resources, or files, as password protection, memory management, virus protection, disk repair, screensavers, font and icon tools, desktop enhancements and file compression. Translators There are two main language translators: Compiler – Translates a computer program from one language into another prompting you if any error is found. It then converts your source code (written in human language) to a language that the computer understands (machine language or object code). Interpreter – An interpreter converts the code during run time, it converts the code one line at a time then execute that instruction at the same time. APPLICATION PROGRAM Application program is used to solve specific user task. This software constitutes the greatest proportion of software used on a computer system. Task carried out by application software include: Calculating Payroll Preparing Word Processing documents Playing games Research Information Application software falls into the following categories: General-purpose Custom written Customization of general-purpose Specialized Integrated General Purpose Software General-purpose software or “off the shelf” software may be used by many different persons for many different tasks. The most popular general-purpose software is: Word processing packages – software package used to create text documents. Spreadsheet packages – A spreadsheet is an electronic work sheet of rows and columns that is used to manipulate numbers Games
You can install it yourself by following the easy instruction in the in the installation manual that comes with the software. Easy updating and revising, each new version can be had at a reduced price if the owner can show proof of purchase of a previous version. Most users are familiar with the previous versions of the software, so no intensive training is required. Several persons use the software, therefore help is easy to find. Disadvantages of general-purpose software The package may be poorly documented. The package may have hidden problems The package may not fit the user’s exact needs. The package may not be user friendly. Custom written Custom Written Software is software that is created by a professional programmer of an organization. The software meets the specific need of the user or organization. Custom written software is needed because most businesses have some procedures that are unique to its operation. Advantages of custom written The software meets the need of the user specifically. The software can grow with the company/ Business owners can relieve the stress placed over burdened employees and save money hiring additional staff. Disadvantages of custom written Expectation can change midstream when custom written software, making a realistic difficult to project. As a result, a business often out of money before the project is complete. An experienced software team is needed. Acquiring the right team can be costly. If the people who are trained to use the resign then it will be some time before new are trained, slowing down the business functions. Customisation of general purpose software General purpose software packages may be purchased (off-the-shelf) and then modified to meet the organization’s needs. Not all general purpose software is customizable, but there are some that are created with the option that the buyer can customize certain aspects of the software to meet their needs. Areas of the software that can be customized include: Screen Color, Page size and arrangement on the desktop, Navigation to available menus Specialized Software These are software that is created for a specific discipline. A doctor might use such a program to aid in process of diagnosis or an engineer might use such software to design a house and test the design using same software. Advantages of specialized software Permanent will not migrate or resign. Easy to transfer from one application to another. Easy to document. Consistent, not unpredictable. Cheaper Disadvantages of Specialized Software Lack of inspirational ability Must be constantly fed new data Limited only to data input Integrated Software This is a Software package that combines many applications, in one program. Integrated packages can move data among several programs utilizing common commands and file structures. In integrated software (such as Microsoft Office, the output of one program (such as a spreadsheet or graphics program) can be readily imported into or embedded in another program (such as a word processor ). Integrated software is best suited for applications with the following: --business processes with overlapping data requirements --aka data created in one step is needed to complete others Advantages Easier to learn the different applications as they have a common look & feel. superior scalability over time lower cost of ownership for an integrated package than to buy individual applications USER INTERFACE The user interface is what is presented between you (the user) and your computer. It allows the user to interact with the computer. There are three types of user interface, these are: 1. MENU DRIVEN 2. COMMAND LANGUAGE INTERFACE 3. GRAPHICAL USER INTERFACE (GUI) Menu Driven A menu gives the user a list of commands from which to choose from which to choose or request the data to be entered in a particular form. A software package that uses menu is said to be menu-driven. A mouse is used to select options from a pop-up or drop-down menu. The main interfacing device for this user interface is the mouse although a keyboard can also be used to select options. A  dvantages of Menu driven interface
The user is presented with a list option to choose from, they don’t need to remember commands. Free from typing errors, because user do not have to type a command. A wide variety of input device can be used to interface with menu. Disadvantages of Menu driven interface Several steps required to issue a command Once user has learned the menu system it is bothersome to have to wait on the package to be presented with the questions before commands can be entered. C  ommand Language Interface
A command driven package simply waits for the user to type in the appropriate commands of data. It may show a prompt to indicate to the user where commands or data are to be entered. Using a command driven package requires that the user learn the necessary commands or take classes in using the package. An example of a command driven software is MSDOS. The main interfacing device for this user interface is the keyboard. Advantages of command driven interface Faster to use once you have learnt the commands For computer programmers command driven interface are cheaper to implement Disadvantages of command driven interface It is sometimes difficult to remember all the commands, therefore users have to constantly refer to the software user manual Restrict the user to using only the keyboard as the interfacing device. Command must be entered at a special location. G  raphical User Interface
A GUI (graphical user interface) consists of Windows, Icons, menus, Prompts (WIMP) There are "pop-up" and "drop down" menus. A mouse is used to click on an icon to execute some operation or select option from a pop-up or drop-down menu. The main interfacing device for a GUI is the mouse. Advantages of GUIs User friendliness results in less anxiety on the part of the user. Icons / symbols are easier to recognize and provide the user with a context. Fewer command error. Reduce typing Disadvantages of GUIs May consume more screen space For programmers the design of the GUI is more complex Clicking an icon can produce unexpected result because of lack of icon standard Increase use of computer memory can lead to slower processing PROCESSING METHODS When data have been collected and is ready to be processed, data is processed in either one of two ways, namely: a. Batch Processing b. Real-Time Processing BATCH PROCESSING In this processing method, data is collected over a period of time and is processed periodically. The good thing about Batch Processing is that the grouping of data and the periodic processing of jobs make more efficient use of the resources of the computer, compared to allowing data and jobs to be processed in an unorganized and random manner. Of course, this efficiency and economical way of processing data comes with the sacrifice of the immediate processing and to acquire up-to-date data is not always possible. Examples of Batch Processing In a typical example, the banking industry accumulates all cheques deposited each day into batches and at the end of each day; they will up-date the customer’s account with the amount deposited. Therefore, a customer’s bank account is updated daily, and many management reports may be prepared at the end of banking operations each day. In a Batch Processing System, the data collected and stored over a period of time is called Transaction Data. Batch Processing Systems are normally associated with Transaction Processing Information Systems. Advantages Batch Processing is an economical method when large volumes of transaction data must be processed. It is ideally suitable for many applications where it is not necessary to update database records as transactions occur, and where documents and reports are required only at scheduled intervals such as Payroll Preparation which might be done weekly, bi-weekly or monthly. Use to process a large amount of information. Makes more efficient use of the computer resources. Most cost-effective method to be used to process data. Disadvantages Master files are frequently outdated between scheduled processing date/time, as only the periodic scheduled reports are produced. Takes more time to process data in batches (groups). REAL TIME PROCESSING Real Time Processing capability allows transaction data to be processed immediately after they are generated and provide immediate output to end users. Full-fledged Real-Time System for transaction processing is popularly called On-line Transaction Processing (OLP) Systems. Transaction data are processed as soon as they originate or are recorded, without waiting to accumulate batches of data. Data are fed directly into the computer system from on-line terminals, without being sorted and they are always stored on-line in direct access files. Files and databases are always up-to-date since they are updated, regardless of there frequency of use. Responses to end users’ enquiries are immediate, since information is stored on direct access storage devices, which can be retrieved instantaneously. Real-Time Processing depends on Wide Area and Local Area Network to provide telecommunications links between transaction terminals, workstations and other computers.
An example of Real-Time Processing (Sales Transaction Processing System) is where Customers, product and sales databases are stored on on-line direct access storage devices (typically Magnetic Disks) and can be updated immediately to reflect sales transactions. Advantages Real time processing provides immediate updating of files and immediate responses to user enquiries. Real time processing is particularly important for applications where a high frequency of changes must be made to a file during a short time, to always keep the file up-to-date such as in Airline Reservation Systems. There is continual and rapid processing of data. Instant feed back is available upon data processing after input of the data is done. Immediate and direct communications between end-users and the computers. Example: British Airways or Air Jamaica Flight Reservation Systems. Disadvantages Because of the online, direct access nature of Real Time Processing, special precautions must be taken to protect the contents of databases from lost of data or data corruption. Real Time Processing Systems uses Magnetic Tapes as control logs (to record all transactions made) or as back up and so data is kept on two different storage mediums that can be considered expensive in the long run. More control has to be built into the software and processing procedures to protect against unauthorized access or the accidental destruction of data. DATA COMMUNICATION DEVICES AND MEDIA Data Communication – is the process of transmitting data and information over a communication medium such as a standard telephone line, coaxial cable, fiber optic cable, or microwave, between one computer terminal and another. Many computer users need to be able to connect their computer to other computers, whether located close by or at a remote site. For example, office workers may want to communicate with computers at their workplaces from wherever they may want to access the Internet. Data communication is essential for electronic mail (e-mail), voice mail, facsimile (fax), telecommuting, videoconferencing, electronic data interchange (EDI), global positioning systems (GPS), bulletin board systems (BBSs), on-line services and the Internet. Many schools, business and other organizations link computers together to form a network so that they can transmit data and information to share files. Resources such as: disk drives, CD-ROM drives, modems or printers and programs such as word processors, spreadsheets and databases. Computers can be linked in different ways, or configurations, to transmit data. Two configurations are: Point-to-point Transmission This is a direct transmission between a sending and receiving device. It may be one of two types: A switched, dedicated. Switched:- Uses regular telephone lines to establish a communication connection. Each time a connection is made, the line to be used for the call is selected by the telephone company switching station (hence the name switched line). Dedicated:- This is a line connection that is always established. The communication device at one end is always connected to the device at the other end. A user can create his or her own dedicated line connection by running a wire or cable between two points, such as between two offices; buildings or dedicated lines can be provided by an outside organization. Broadcast: using one computer to transmit data and information to serve the needs of several terminals or computers connected to it in a network Telecommunication – is the transmission of data over a far distance without changing it. A telecommunication system contains the following components: A Sender – One who creates the information to be transmitted. A Medium – the physical path between sender and receiver A Receiver – who receives the transmitted information unchanged TRANSMISSION MEDIA T  ransmission media refers to the physical material along which data travels from one point to another eg. cables. The media used is dependent on the distance of the data to be transmitted. For short distance communication, computers are linked by cables. Three types of cable used are: twisted pairs, coaxial cables and fiber optics. For communication over long distances, wireless technology is used, for example, microwave, and satellites.
SHORT DISTANCE TRANSMISSION MEDIA Twisted Pairs This cable consists of a twisted pair of copper wires and is the medium used by telephones to transmit data. Advantages The telephone network links the entire world; therefore, data can be transmitted to virtually any place in the world. Cheap. Disadvantage Subject to interference. Coaxial Cable consists of a conductive cylindrical shield with a central wire o  r solid core held together by an insulating material. These are the cables that connect your television set to the cable television provider and one medium used to connect computers in a local area network.
Advantages • Non-susceptible to interference. • Transmits faster than twisted pairs. • Can accommodate digital and analog signals. D  isadvantage
• Heavy and bulky. • Needs booster over distance.
A Fibre optic line is made up of tiny threads of glass tubes about the size of a human hair. Large volumes of data can be transmitted at the speed of light through these glass tubes. A single glass fibre can transmit the entire Bible in a single second. Advantages
Smaller and lighter Faster (matches the speed of light) No interference An abundance of raw material to manufacture medium Able to bend light around corner Disadvantages Expensive Hard to install and modify LONG DISTANCE COMMUNICATION MEDIA Microwave transmission Media 
Microwave is a good medium for sending data between buildings in a city or on a large college campus. For longer distances, the radio waves must be relayed by means of “dishes”, or antennas. These can be installed on towers, tall buildings and mountain tops. Advantages • Travels at the speed of light. • Transmits both analog and digital data.
• Cannot travel around bends (line-of-sight only) • The signal cannot penetrate buildings or mountains • The relay stations must be placed no re than 30 miles apart. 
Satellite A communication satellite acts as a relay station in outer space. It is placed in orbit over 23,000 miles above the earth surface. It receives data beamed at it from a ground station and sends that data to other ground stations. A single satellite in orbit at 22.300 miles can easily cover 40% of the earth’s surface It is possible to relate data from satellite to satellite and then beam it to any ground station on earth. Advantages Always in sight. No distance limitation. Disadvantages Very expensive to set up Not suitable for rapid exchange of data, because delays occur when data are sent thousands of miles up into space and back down again
A network is a set of computers and peripherals such as printers, plotters, disk drives and modems that are linked together on a permanent basis so that they can communicate and share resources. This could mean two computers on a desk or thousands of computers across the globe, as in the case of the Internet. Advantages of Networks Enable users to share hardware like scanners and printers. This reduces cost by reducing the number of hardware items bought. For example, instead of buying several printers, one good printer could be bought and linked into the network. Allow users access to data stored on other computers. This keeps everyone up-to-date on the latest data, since it is all on the same media, rather than having to make copies of the files, which are immediately out-of-date. Allow users to run programs that are not installed on their own computers, but, are installed somewhere in the network. This reduces the effort for networks administrators to keep programs configured correctly and saves much storage space. Disadvantages of Networks Accessing anything across a network is slower than accessing your own computer. More complexity creates new problems to handle Less customization is possible for shared programs and folders. Everyone will have to follow the same procedures for storing and naming files so others can find the right files. .NETWORK CONFIGURATIONS Networks come in different sizes. A few computers, printers and large hard disks, usually on one site, when linked over a small geographical area is called a local area network (LAN). Computers linked over a large geographical area is called a wide area network (WAN). A classic example of a wide area network is the Internet. A Metropolitan Area Network (MAN) falls between a WAN and LAN. It is large enough to extend to an area like a city o town. A MAN might therefore be owned and operated by a single organization MANs are useful in connecting LANs to wide area networks like the Internet. Computers that are not networked are known as stand-alone computers. Data that is on a stand-alone system has to be transferred by disk if it is to be used on another computer. Network Topologies The topology of a network is its physical layout. This is how the computers or terminals are linked together to form the network. There are three main types of layout (topology) of computer networks: star, bus and ring.  In a star network all the nodes are connected to a central hub which is the computer that handles the network’s tasks and holds the data. Communication flows through the host. This means that each computer has its own connection to the network and that a break in a cable will not affect the working of other computers. If the hub breaks down, then all the computers on the hub will not work.
Advantages • Gives close control of data. • Each PC sees all the data. • Data received by the user is always up-to-date.• Computer other than the host fails, no other computer is affected. Disadvantage •  Should the host computer or its software malfunctions, the whole network is down. (A backup computer system would be necessary to keep the network going while repairs are made to the hub).
BUS TOPOLOGY A bus network is the simplest type of topology, where the network nodes (computers) are connects the computer to the same communication line. Communication flows in both directions along the line. All the computers can communicate with each other without having to go through the server. Bus networks are cheap and reliable, but if the cable breaks the network is split into two unconnected parts. Bus networks are slower than star networks, with the speed of network traffic limits to 10 Mb per second. Advantage If one of the computers or devices should stop working, this will not affect the others Disadvantage C  annot connect a large number of computers this way. For instance it is physically difficult to run the one communication line over a whole building.
A ring network has no end to the line. The last node (computer) is connected to the first node, forming a ring or loop. There is no central host computer that holds all the data. Communication flows in one direction around the ring. As with a bus network, if the cable breaks it will affect all the computers on the network. This configuration is good when the processing of data can be done on the local PC. Ring networks are also slower than star networks, with the speed of network traffic limited to 10Mb per second. Advantage Requires less cabling and so is less expensive. Disadvantage • If one node is down, the entire network will not be able to function Communication Modes The direction of transmission is classified in three ways: Simplex - Data flows in one direction only. Simplex is used only when the sending device, such as temperature sensor, never requires a response from a computer. Half-Duplex- Data can flow in both directions but only one direction at a time. Eg. A walkie Talkie. The user can talk or listen but not do both at the same time. Full-Duplex - Data can be sent in both directions at the same time. A normal telephone line is an example. Both parties can talk at the same time. TRANSMISSION SIGNALS Data transmitted over a network exists in one of two forms: Anolog Digital
Analog Signals are what we encounter every day of our lives. Speech is an analog signal, and varies in amplitude (volume) and frequency (pitch). The main characteristics of analog signals are: DIGITAL SIGNALS Digital Signals are the language of modern computers. They normally comprise only two states, expressed as ON or OFF, 1 or 0 respectively. Modem (Modulator/Demodulator)- A modem is a communications device that can be either internal or external to your computer. It allows a digital computer to connect an analog device and vice versa, and transfer data. Bandwidth The transmission rate (Speed) of a communications channel is determined by its bandwidth. It is the range of frequencies that a channel can carry. Because transmitted data can be assigned to different frequencies, the wider the bandwidth, the greater the frequencies. Thus more data can be transmitted at the same time. Broadband – This is speed greater than that of an ordinary telephone line. It is capable of transmitting data at speeds of over 100000 cps per second. Narrowband- This is speed equal to or less than that of an ordinary telephone line, about 64 kilobits per second or less or 10 to 30 cps. Voiceband - A communication channel that can transmit data at a rate of 1000-8000cps eg. Telephone line. DATA COMMUNICATION TERMS Hotspot-A hotspot is any location where wireless internet access is made publicly available. You can often find hotspots in airports, hotels, coffee shops, and other places where business people tend to congregate. Infrared is short wave electromagnetic radiation which allows computing devices with infrared ports to communicate. They must be within line of sight of each other and data can only be transmitted over a short distance. Signals cannot penetrate walls or other obstructions. Scattered infrared communication is a broadcast f infrared transmissions sent out in multiple directions that bounces off walls and ceilings until it eventually hits the receiver. Wi-Fi - “Wireless Fidelity." refers to wireless networking technology that allows computers and other devices to communicate over a wireless signal. These devices use a built in Wi-Fi card to connect to a wireless router. Bluetooth is wireless technology that uses radio waves to enable communication between Bluetooth-compatible devices. It is used for short-range connections between desktop and laptop computers, PDAs (like the Palm Pilot or Handspring Visor), digital cameras, scanners, cellular phones, and printers etc. A domain name is a unique name that identifies a website eg courts.com. The website domain name serves as an address, which is used to access the website. When you visit a website, the domain name appears in the address bar of the web browser. All domain names have a domain suffix, such as .com, .net, or .org. The domain suffix helps identify the type of website the domain name represents. Examples .com domain names used by commercial website. .org used by non-profit organizations. .gov used by government institutions .net used by internet organizations .edu used by educational institutions Some domain names end with a country code, such as ".dk" (Denmark) or ".se" (Sweden), which helps identify the location of the website. Social networking websites allow users to be part of a virtual community. The two most popular sites are currently Facebook and MySpace. These websites provide users with simple tools to create a custom profile with text, pictures, basic information about the user and possibly a blog or other comments published by the user. Profiles may include videos, photo albums, online applications (in Facebook), or custom layouts (in MySpace). After creating a profile, users can add friends, send messages to other users, and leave comments directly on friends' profiles. E-commerce (electronic-commerce/e business) refers to business over the Internet. Web sites such as Amazon.com, Buy.com, and eBay are all e-commerce sites. A cookie is a small amount of data generated by a website and saved by your web browser. Its purpose is to remember information about you, such as your login and username. IP address (Internet Protocol Address) is a code made up of four sets of numbers from 0 to 255, separated by three dots that identifies a particular computer on the Internet. Every computer, requires an IP address to connect to the Internet. Examples"66.72.98.236" or "216.239.115.148". The domain name of a website translates to its IP address. A newsgroup is an Internet-based discussion about a particular topic. These topics range from sports, cars, investing, teen problems etc. Users post messages to a news server which then sends them to other participating servers. Then other users can access the newsgroup and read the postings. The groups can be either "moderated," where a person or group decides which postings will become part of the discussion, or "unmoderated," where everything posted is included in the discussion. To participate in a newsgroup, you must subscribe to it. Spam refers to junk e-mail or irrelevant postings to a newsgroup or bulletin board. The e-mail messages you receive about refinancing your home, reversing aging, and losing those extra pounds are all considered to be spam. A wiki is a Web site that allows users to add and update content on the site using their own Web browser. This is made possible by Wiki software that runs on the Web server. Wikis end up being created mainly by a collaborative effort of the site visitors. A great example of a large wiki is the Wikipedia, a free encyclopedia in many languages that anyone can edit. Blog refers to an online journal or diary of an individuals opinions or news. It is a list of journal entries posted on a Web page by the blogger or by individuals making comments. Downloading is the process in which data is sent to your computer. Whenever you receive information from the Internet, you are downloading it to your computer. Uploading is sending a file from your computer to another system. Netiquette, or net etiquette, refers to etiquette on the Internet. Good netiquette involves respecting others' privacy and not doing anything online that will annoy or frustrate other people Protocol is a common set of rules and instructions that each computer follows during data communication. Search Engines like Google, Excite, Lycos, AltaVista, and Yahoo are all search engines index and create databases millions of sites on the Web, so that Web surfers can easily find Web sites with the information they want. Search engines can locate relevant Web sites when users enter search terms or phrases. Vlog is short for "video blog" is a blog, or web log, that includes video clips. It may be entirely video-based or may include both video and written commentary. VOIP "Voice Over Internet Protocol," is a telephone connection over the Internet. The data is sent digitally, using the Internet Protocol (IP) instead of analog telephone lines. This allows people to talk to one another over long-distances and around the world without having to pay long distance or international phone charges. A Web site is a collection of Web pages. For example, Amazon.com is a Web site, but there are millions of Web pages that make up the site. Web pages are what make up the World Wide Web. These documents are written in HTML (hypertext markup language) and are translated by your Web browser. A Web page is an individual HTML document. Home Page - This is the starting point or front page of a Web site. This page usually has some sort of table of contents on it and often describes the purpose of the site. A Web browser, often just called a "browser," is the program people use to access the World Wide Web. It interprets HTML code including text, images, hypertext links, Javascript, and Java applets. Some common browsers are Microsoft Internet Explorer, Netscape Communicator, and Apple Safari. A Web server is a computer system that hosts websites. It runs Web server software, which provides access to hosted webpages over the Internet. Most Web servers are connected to the Internet via a high-speed connection. The World Wide Web, or just "the Web, is a subset of the Internet. The Web consists of pages that can be accessed using a Web browser. HTTP "HyperText Transfer Protocol" is the protocol used to transfer data over the World Wide Web. That's why all Web site addresses begin with "http://". URL (Uniform Resource Locator) is a web address. It is the address of a web page or site. Each web pages has its own URL. HTML (Hypertext Markup Language) is the language that Web pages are written in. Also known as hypertext documents, Web pages must conform to the rules of HTML in order to be displayed correctly in a Web browser. The HTML syntax is based on a list of tags that describe the page's format and what is displayed on the Web page. The Internet spreads across the globe and consists of countless networks and computers, allowing millions of people to share information. The internet offer services such as Telnet, FTP, Internet gaming, Internet Relay Chat (IRC), e-mail and the World Wide Web. An Intranet is an internal or private network that can only be accessed within the confines of a company, university, or organization. An extranet actually combines both the Internet and an intranet. It extends an intranet, or internal network, to other users over the Internet. Most extranets can be accessed via a Web interface using a Web browser. Since secure or confidential information is often accessible within an intranet, extranets typically require authentication for users to access them. Extranets are often used by companies that need to share selective information with other businesses or individuals. For example, a supplier may use an extranet to provide inventory data to certain clients, while not making the information available to the general public. Email- An email is a service offered by the internet that allows the sending of letters and other documents quickly and cheaply. To send an email, the sender and receiver must have an email address. Telnet is a TCP/IP protocol used for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely. On the Web, HTTP and FTP protocols allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer. File Transfer Protocol (FTP) is a simple network protocol used to transfer large files between two computers on the Internet. Podcast A podcast is an audio or video program formatted to be played on the iPod and made available for free or for purchase over the Internet. E-Learning - This is education via the Internet, computer network, or standalone computer. E-learning is the transfer of skills and knowledge over a computer system. E-learning refers to using electronic applications and processes to learn. This includes Web-based learning, computer-based learning, virtual classrooms and digital collaboration. Content is delivered via the Internet, intranet/extranet, audio or video tape, satellite TV, and CD-ROM. Bulletin Board An electronic communication system that allows users to send or read electronic messages, files, and other data that are of general interest and addressed to no particular person. Bulletin boards were widely used before the Internet became popular, and many of their functions are now served by websites and newsgroups for specific topics or groups. Instant Messaging/Internet Relay Chat allows user to exchanges text messages in real time over the internet. Some messaging services allow the exchange of files, videos and images. Videoconferencing- Having a meeting using the internet and video software. This allows cheap communication and exchange of ideas with no distance limitations. This allows persons to save on travel cost. Teleconferencing- Teleconferencing is communication between a group of persons (three or more people in two or more locations) through an electronic medium. Telemarketing- This is the selling of goods over the telephone or internet. Telecommuting- Working from home using the internet to connect to the work place, allows persons to work at their own pace, set their own schedule and save on travel cost. Persons however may lose the benefit of interaction with others. COMPUTER SECURITY Computer security is the protection of computer resources from intentional or accidental damage. The resources of a computer includes: Computer hardware, software, data and users. Threats to computer resources:
Direct Crimes include: Theft of Hardware: computers have small expensive parts that can fit into purse or handbags which can easily be stolen, and remain undetected for a while. Theft of Computer Time: This is using the computer of the job to play games and to conduct personal businesses for pay. Theft of Information: This is the illegal copying and selling of confidential company information to competitors ( or the stealing and selling of exam papers to students before exams. Crimes of Revenge: Disgruntled employees can directly attack computers by transferring viruses, formatting hard drives and pouring liquid into system unit. Viruses and vermins A virus is a computer program that is designed to corrupt the files on a person’s computer, and/ or prevent the computer form working properly. E.g. Antichrist etc. Worms travel through the computer’s memory and alter the data it accesses. A Trojan horse is a program that on the surface seems harmless, but, covertly performs malicious acts. Electronic Eavesdropping: This is the tapping of a communication channel to retrieve information. Although not a crime, persons should be aware that they are constantly under surveillance when on the computer. Surveillance is the monitoring of persons computer activities. This is done not only by law enforcement but also by many websites. This is used by websites to develop profiles of persons. Power Surges and spikes there are times when the electricity that powers a computer may have an increase in power due to lighting or other events. This may damage a computer and cause it to malfunction. To protect against these surges in power, the following devices are usually utilized: Surge Protectors- Regulates the amount of power going to the computer in order to protect it from sudden pikes or surges. A Voltage Regulator- Controls fluctuations in voltage, so it cannot affect the computer. Uninterruptible Power Supply(UPS)- this is a battery that continues to supply power to a computer for a limited amount of time, when there is a power cut. This prevents the loss of data and allows users to save their work before total power is lost. Theft by computers Computers are being used to steal money, information, goods and computer services. Here are two examples: A programmer in a bank modified a program to bypass the checking of the overdraft limit on his account. He then drew money from his account without a limit being imposed. A student stole her teacher's computer account password by spying. She then made a copy of the examination questions file from her teacher's computer account. Computer Crimes on the internet Computer network break-ins/ Hacking Using software tools installed on a computer in a remote location, hackers can break into computer systems to steal data, plant viruses or Trojan horses, or work mischief of less serious sort by changing user names or passwords. Network intrusions have been made illegal by U.S. federal government. Industrial espionage is where Corporations, like governments, spy on the enemy. Networked systems provide new opportunity for this, as hackers for hire retrieve information about product development and marketing strategies, rarely leaving behind any evidence of the theft. Not only is tracing the criminal labor-intensive, convictions are hard to obtain when laws are not written with electronic theft in mind. Software Piracy: this is the illegal copying of copyrighted computer software. These copies work as well as the originals, and sell for significantly less money. Piracy is relatively easy, and only the largest rings of distributors are usually caught. Moreover, software pirates know that they are unlikely to serve hard jail time when prisons are overcrowded. Mail bombings Software can be written that will instruct a computer to repeatedly send electronic (email) to a specified person’s email address, the cyber criminal can overwhelm the recipient’s personal account and potentially shut down entire systems. This may or may not be illegal, but it is certainly disruptive. Spoofing is the act of disguising one’s computer to electronically “look” like another computer in order to gain access to a system that would normally be restricted. Credit card fraud Bulletin boards and other on-line services are frequent targets for hackers who want to access large databases of credit card information which is then used to make purchases. Propaganda is the use of computer technology to spread propaganda, political, beliefs, agendas and ideals as well as attack other person’s beliefs. Securing Computer Resources There are techniques developed to protect single computers and network-linked computer systems from accidental or intentional harm, including the destruction of computer hardware and software, physical loss of data, deception of computer users and the deliberate invasion of databases by unauthorized individuals. Computers and the information they contain are considered confidential because their use is typically restricted to a limited number of users. Confidentiality and the possession of information can be violated by shoulder surfing, or observing another user's computer screen; tricking authorized users into revealing confidential information; wiretapping, or listening in on or recording electronic communications; and stealing computers or information. A variety of simple techniques can prevent computer crime. For example, destroying printed information, protecting computer screens from observation, keeping printed information and computers in locked cabinets, and clearing desktops of sensitive documents prevent access to confidential information. But more sophisticated methods are also necessary to prevent computer crimes.
A door can be locked and only someone with a key can enter through the door depending on how the lock is configured. Mechanical locks and keys do not allow restriction of the key holder to specific times or dates. Access Cards or ID cards can be used to authorize access. Biometric Systems the use of biological characteristics to prevent or grant access such as iris or retina scan, fingerprint scan, facial scan or the use of voice activated commands. A password or code can be keyed in to gain access. Passwords are a common means of verifying a user's identity before access is given. Manual Logins (signing in) and security guards can also be used to verify who gains access to secured areas. The use of security cameras can be used to track who enters facility as well as allow the viewing of their activities while there. Secure Locks and lids can be used to prevent the detachment of computer parts all well as prevent access to the system unit. Fireproof and Waterproof cabinets can be used to prevent damage to files and data stored in them in the event of a fire or flood. Software Access Restrictions: This is the process of restricting access to software. This is done using passwords, encryption or for commercial software installation keys, that requires the user to enter a serial number (key) before installation can take place. Data security is the system of safeguards that protects software and data from theft or modification. Methods of protecting software include: Encryption: IS the process of encoding information so it bears no similarity to the original information, in order to secure it. Files are then decrypted (decoded) in order read the information. Passwords: Is a special code that is used to prevent unauthorized access to file or computer system. Users must have code to access file or system. Anti- virus programs: This is a special type of software that tries to detect and remove viruses that are on a computer or removable storage. Approved Users Another technique to prevent computer crime is to limit access of computer data files to approved users. Access-control software verifies computer users and limits their privileges to view and alter files. Records can be made of the files accessed, thereby making users accountable for their actions. Military organizations give access rights to classified, confidential, secret, or top secret information according to the corresponding security clearance level of the user. Tokens are tamper-resistant plastic cards with microprocessor chips that contain a stored password that automatically and frequently changes. When a computer is accessed using a token, the computer reads the token's password, as well as another password entered by the user, and matches these two to an identical token password generated by the computer and the user's password, which is stored on a confidential list. Firewalls Computer networks, multiple computers linked together, are particularly vulnerable to computer crimes. Information on networks can be protected by a firewall. The firewall prevents unauthorized users from gaining access to the computers on a network, and it ensures that information received from an outside source does not contain computer viruses, self-replicating computer programs that interfere with a computer's functions. Backup and Recovery refers to the process of making a permanent copy of data in case of a loss and setting up systems that allow that data recovery after data loss. Backing up data requires copying and archiving computer data, so that it is accessible in case of data deletion or corruption. Archiving Data archiving is the process of moving data that is no longer actively used to a separate data storage device for long-term retention. Data archives consist of older data that is still important and necessary for future reference, data archives protect older information that is not needed for everyday operations but may occasionally need to be accessed. Integrity and Authenticity The integrity and authenticity of information are threatened by modifying, removing, or misrepresenting existing data. For example, omitting sections of a bad credit history so that only the good credit history remains violates the integrity of the document, and requesting a cash advance using a stolen credit card violates the authenticity of that transaction.. Availability The availability of information is affected if access to the information is prevented; if data are moved, misplaced, or damaged; or if information is converted to a less useful form. Computers and components such as floppy or hard disks are easy to damage. A computer's memory can be erased or the computer's hardware can be damaged by flooding, fire, or dust. To safeguard the availability of information, several backup copies of data should be made and stored in another location. Businesses that rely on computers need to institute disaster recovery plans that are periodically tested and upgraded. Proprietary data is internally generated data that contains technical or other types of information owned exclusively by a firm to safeguard its competitive edge. Proprietary data may be protected under copyright, patent or trade secret laws. Propriety software is computer software which is the legal property of one party. The terms of use for other parties is defined by contracts or licensing agreement. Eg. of proprietary software are Microsoft Windows, Real Player and I-tunes. APPLICATION AND IMPLICATIONS OF COMPUTERS Computers in Education Computers can be used as a tool for enhancing the process of learning. They may also play an important role in searching information and school administration. .Here are some hardware requirements: PCs and possibly a server in a larger institution printers and scanners speakers, microphones and other peripherals. Speakers, microphones and other peripherals help people with disabilities and may be needed for some educational software. Here are some software requirements: general-purpose software that can help students write and prepare assignments and projects educational software that allows students to create timetables and other administrative tools database software for keeping student records, such as educational management information systems (EMIS) software required to run educational programs and simulations. Computer Assisted Learning (CAL) Computer assisted learning is the use of computers in assisting learning. For example, a student may use a drill-and-practice program to practice what he/she has just learnt from a lesson or use a tutorial program to enhance a skill or learn about a subject. Advantages Educational software helps students understand a subject better. Some software can simulate science experiments. Learners who have disabilities can take lessons and courses using specially designed computers and software. Screen readers can read out the text on a computer screen to visually impaired students. Any person can take e-learning courses at home in their own time on a computer with internet access. The multimedia contents, such as special sound effects, animation and video can arouse students' interest in learning. Tedious practices in arithmetic and spelling can be turned into entertaining games. This makes learning more exciting and interesting. Some CAL software includes testing and diagnostic features which allow teachers to identify common misconceptions of their students. CAL can provide immediate feedback to students. The automatic grading of exercises feature frees up teachers' resources that can be used for additional attention toward students. Students can learn at their own pace. This alleviates the pressure on the slow learners so that they can keep up with their peers. Students are free to make wrong answers because there is no peer group pressure. This encourages them to learn by trials and errors. Multimedia contents can help make difficult or abstract concepts simple. OTHER USES Searching information on the WWW using search engines. Searching information on a CD-ROM/ Dictionaries, encyclopedias, maps and other specialized references are now available in CD-ROMs. Many of them also include multimedia capabilities. Cyber schools A cyber school is a school that uses the Internet as a delivery tool to offer courses. The course materials and video lectures are made available on the Web. By utilizing video-conferencing, tutors can talk to students in various locations and answer their questions in real time. Students can also exchange ideas through interactive discussion groups. What are the advantages of cyber schools? Students can attend classes anytime, anywhere, and anyplace. Handicapped students can attend classes without commuting. The tuition fee of cyber schools is usually lower than that of the traditional schools. Administrative tools Computers can be used with software that provides a computerized network system to schools for supporting the administrative and management processes, and for transmitting electronically, information between schools. Some of the major functions which can be carried out includes: To maintain school information. To collate data for the preparation of statistical reports and forms. Students' records and attendances To maintain students' personal, performance and extra-curricular information. To create students' assessments To print students' assessment reports. To maintain teachers' and staffs' personal and duty information. To keep records of staffs' absences. To automate the process of deploying substitute teachers. To schedule timetables which show lesson arrangements for classes, teachers and venues respectively etc. Computers in Recreation Recreation is another area of computer application. You can play electronic games at home. You can play chess with the computer as your opponent. Some software combines entertainment and education called Edutainment. Computer special effects in movies The characters in Toy Story are computer generated. The animators have to animate each and every move the characters made. Pixar wrote a computer program called RenderMan to produce all the animation. This program enables animators to handle extremely large renderings with relative ease. This movie is animated solely by computers. Scenery A film director may need scenery that does not exist in real life. For example, a scene with the Tower Bridge (in England) appearing in Victoria Harbour (in Hong Kong). With the help of computers, pictures of Victoria Harbour can be combined with the digital image of the Tower Bridge to produce this special scenery. Here are some recreational pastimes where people use computers:
displaying and editing digital photos, such as holiday photos surfing the Internet to find out about things that interest them playing music and putting together their own compilations and playlists to play on an MP3 or MP4 player listening to a live radio broadcast as streaming audio using a computer and the Internet playing a variety of realistic-looking games that cover sports, combat, strategy, driving, flying any many other themes. You will need the software for your chosen recreation. For example, to edit photos you will need photo-editing software such as Adobe Photoshop. editing and creating videos they can burn on to DVD The hardware requirements also depend on what you want to do: For gaming and anything involving graphics and photos, you need a personal computer with a graphics and 3D card. To print out photos and pictures, you need a colour printer. To burn CDs and DVDs, you need CD and DVD writers. Games may also require joysticks and other peripherals that help you play the game, such as a steering wheel. The music industry uses computer technology to create and edit music. Recording studios can use computers to modify the quality of music, as well as merge different layers and sounds, and add sound effects. Several programs allow you to record your own music then edit and modify it. Computers in Business Applications Computers are widely used in business nowadays. Software used in Business Applications General-purpose software such as Microsoft Office. Businesses can choose open-source software, which is software that is freely available, such as OpenOffice. They can choose to use proprietary software, which is software that you pay for. Some open-source software may be less stable than proprietary software. Internet access, web browsers and e-mail programs. Accounting software to keep track of the financial records of a company. Software customized for that environment. A company that designs websites may have their own range of website design tools. A financial institution may use special accounting software to keep track of financial records. Here are some probable hardware requirements: personal computers (microcomputers) for each user network infrastructure to link the PCs printers fax machines. Some businesses do telemarketing over the telephone. Telemarketing is where goods are bought or sold over a communication channel. Telemarketing can also be done through websites that allow people to browse products. Teleconferencing allows people to conduct meetings over the telephone or the Internet. Several people can participate at once, and you can even use video cameras and other peripheral devices to see participants. This is called videoconferencing. It reduces the need to travel to other cities or offices. Automatic Teller Machine (ATM) An ATM is a terminal specially designed for self-service banking. An ATM can be used to withdraw cash. transfer money from one account to another. pay bills. check account balances. request cheque books and bank statements. change personal identification number. Internet banking helps you to: transfer money from one account to another. pay bills now or schedule future payments. check account balances and transaction history. access previous account statements. request cheque books. initiate stop payment requests. change personal identification number. trade stocks, view major indices and get stock quotes. view currency exchange and interest rates. place fixed-time deposits and change maturity instructions. apply for credit cards and various types of loans. enroll in insurance plans. In order to use Internet banking services, you need: a computer installed with communication device such as a modem. a reliable connection to the Internet through an Internet Service Provider. a secure browser to send and receive information over the Internet. What are the advantages of Internet banking? It provides an access to a variety of banking services 24 hours a day, 7 days a week. The customers can manage their finances anytime, anywhere without visiting the bank in person. It helps to save the bank's human resources, hence reducing the operation cost. Supermarket checkout counter A supermarket uses a POS to compute customer’s transactions. It is a special-function terminal. In retail stores, it is a combination of an electronic cash register and a bar code scanner or reader. What are the advantages of a computerised checkout system? Prices retrieved by the computer from the file are more accurate than being retrieved by typing manually. It is easier to change prices because only updating the computer file is needed. Without the system, repeatedly restamping the price on each piece of the product is required. Checkout is faster. The labour cost is reduced. The computer can keep track of the quantity of each product left on the shelves and in the warehouse inventory; it can inform the manager when restocking and reordering are necessary. The raw sales data collected by the computer can be analysed to discover customer preferences and purchasing habits. Smart cards - A smart card looks like a credit card in size and shape, but instead of a magnetic strip it contains an embedded microprocessor and memory. One popular use of smart cards is its stored value. Each time you use the card, the available of dollar money is reduced. Other applications of smart cards: Smart cards can be used to store personal data and medical information. In case of an emergency, the cardholder can be identified rapidly and doctors or hospitals can then provide improved treatments. Smart cards can be used as keys to log on to an online bank. Smart cards can be used as identity cards for students and employees. Since the identity with access privileges are stored on them, the cardholders can be granted access to certain departments/offices, facilities, equipment and data according to their status. They can also be used to track information such as business transactions or employee attendance. What are the advantages of a smart card? It improves the convenience and security of any transaction. It provides reliable and fast payment. It eliminates the service provider's need to handle heavy coins. This also reduces the operation cost. It provides a convenient way to carry data between systems. Computers in Office Applications The advance of computer technology supports a range of improved office activities. Office automation (OA) Office automation is the use of hardware, software and networks to enhance general office works such as communication among employees, and documents typing and filing. Software in OA Word processing software Sending personalized letters with the help of the mail merge function of word processing software, Software used in Office Administration Includes: Spreadsheet software for creating spreadsheets to maintain accounting records Database management software to record employee or client data. Presentation software used to create presentations for marketing, training etc. Electronic mail (e-mail) for communicating with clients and other staff members. Computers in Industrial Applications Engineers and architects are now designing products with computers. Computer-Aided Design (CAD) Computer-aided design is a term that refers to the use of computers and graphics-oriented software to aid in the design process. CAD systems allow engineers to create two-dimensional or three-dimensional electronic objects. They also enable the designers to view the objects from different perspectives. Example uses of CAD: Vehicle design: For example, the engineers of Nissan Shatai designing a vehicle model using a 3D-CAD system. The system allows the engineer to view the models at different angles. Building design: Architect designing a building model using a CAD system. What are the advantages of a CAD system? It allows a designer to modify the design more easily than traditional manual drafting. It allows a designer to view the object from different perspectives. Hence, the designer does not need to produce a different drawing for each view. It allows a designer to change the size of the object. It reduces the design time. Engineering and design Computer-aided engineering (CAE) is where engineers use computers to help them analyse plans made by CAD. These programs can simulate technical designs to ensure they will work properly in real life, which is an important advantage. Engineers need personal computers with good monitors to create drawings. They need graphics plotters and other printers. They also need CAD and CAE software
Computer-aided manufacturing is a term that refers to the use of computers to control equipment drilling, welding and milling in the manufacturing process. Factories and production plants make extensive use of computers to manufacture goods. Computers can control robots in computer-aided manufacturing (CAM). Robots are machines that carry out tasks. Car manufacturers use CAM and robots to assemble cars. The hardware requirements of a manufacturing organisation are the robots as well as a server and microcomputers. The software would be specialised software to control robots. What are the advantages of CAM?
The computer-controlled robot can perform tasks with precision and it is more accurate than a human. The computer-controlled equipment can perform dangerous and repetitive tasks for humans. The computer-controlled equipment reduces production costs because it does not require any annual leave, sick leave and other fringe benefits. Transportation systems Traffic lights control In order to optimize a traffic flow, a computer system can be used to coordinate the signal timings of the adjacent traffic lights. The system can monitor the traffic flows in real time by collecting traffic flow data from different traffic sensors placed at various locations. . Based on the current traffic flow situation, the system will send signal control instructions to the traffic lights to adjust their signal timings in order to minimize delays and reduce stopping time. Train scheduling A computer is used with a timetabling algorithm to generate a train schedule to dispatch and reverse trains based upon the required train headway (time between two successive trains) at different time periods. Computers in Scientific Applications Computers are used extensively in science. For example, meteorologists use computers to study the formation of tornadoes. Computers can also be used to simulate automobile accidents on screen.. Modeling Computer modeling is the use of computers to create abstract models of real life objects, organisms, situations, or systems. A computer model is not static, you can feed data in and examine how it behaves under certain conditions. Example of Financial modeling A financial manager can create a spreadsheet to project the profit and loss of his company. Simulation of experiments A computer simulation refers to the use of computers to execute a model. It is represented by a computer program that gives information about the object, situation or system being examined. Advantages of computer modeling and simulation: It is much cheaper to use a simulator to train pilots rather than using the real planes or ships. Some demonstrations or experiments are too dangerous to be conducted. A simulation is an alternative. Computer simulations can serve as a time machine for exploring the future. For example, it could take the biologists many years to study whether the rising tiger population in a forest threatens other animals. A computer model of the forest would speed up the biological processes, and the biologists can study their effects over several generations in a few minutes. In many cases, the experiments are required to repeat with different conditions. Replication on a computer model is simple and requires just a matter of changing some input data and running a new simulation. In some experiment simulations, users can control the speed of the simulated motion or process. This facilitates users to see and understand the relationships. Download 2.81 Mb. Share with your friends:
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