Basic Computer Architecture

The main components in a typical computer system are the processor, memory, input/output devices, and the communication channels that connect them.

The processor is the workhorse of the system; it is the component that executes a program by performing arithmetic and logical operations on data. It is the only component that creates new information by combining or modifying current information. In a typical system there will be only one processor, known as the central processing unit, or CPU. Modern high performance systems, for example vector processors and parallel processors, often have more than one processor. Systems with only one processor are serial processor, or, especially among computational scientists, scalar processors.

Memory is a passive component that simply stores information until it is requested by another part of the system. During normal operations it feeds instructions and data to the processor, and at other times it is the source or destination of data transferred by I/O devices. Information in a memory is accessed by its address.

Input/output (I/O) devices transfer information without altering it between the external world and one or more internal components. I/O devices can be secondary memories, for example disks and tapes, or devices used to communicate directly with users, such as video displays, keyboards, and mice.

A bus is used to transfer information between several different modules. Small and mid-range computer systems, such as the Macintosh have a single bus connecting all major components. Supercomputers and other high performance machines have more complex interconnections, but many components will have internal buses.

Communication on a bus is broken into discrete transactions. Each transaction has a sender and receiver. In order to initiate a transaction, a module has to gain control of the bus and become (temporarily, at least) the bus master. Often several devices have the ability to become the master; for example, the processor controls transactions that transfer instructions and data between memory and CPU, but a disk controller becomes the bus master to transfer blocks between disk and memory. When two or more devices want to transfer information at the same time, an arbitration protocol is used to decide which will be given control first. A protocol is a set of signals exchanged between devices in order to perform some task, in this case to agree which device will become the bus master.

Once a device has control of the bus, it uses a communication protocol to transfer the information. In an asynchronous (unclocked) protocol the transfer can begin at any time, but there is some overhead involved in notifying potential receivers that information needs to be transferred. In a synchronous protocol transfers are controlled by a global clock and begin only at well-known times.

Video Conferencing

Video conferencing in its most basic form is the transmission of image and speech, back and forth between two or more physically separate locations. (Imagine a telephone call where you can see the speaker or a television through which you can talk).

How Video Conferencing works?

Cameras simultaneously swap live pictures between the TV screens in each location. Cameras can be set to show the whole room, zoom in on one person or focus on a Whiteboard/overhead projector or a special document camera can be set up to send shots of papers, graphs or overheads. You can view pictures you are sending at the same time using the picture in picture function on the screen. Videotaping of the entire meeting is also available if taping is required. Three or more locations can be connected using multi point Videoconferencing.

Bulletin Board System

Bulletin Board System, or BBS, in computer communications, an online service that enables users to post and read messages, converse by typing messages (“chat”), play games with one another, and copy, or download, programs to their personal computers. There are thousands of BBSs, most organized around a particular topic. Most BBSs are open to the public and free of cost but some can be accessed only by authorized callers.

Chat and Chat Rooms

Chat (online), simultaneous text communication between two or more people via computer. Chat is synchronous—one person types a message on their keyboard, and the people with whom they are chatting see the message appear on their monitors and can respond almost immediately. Other kinds of computer communication are asynchronous. E-mail, for example, may not be delivered or read until minutes or hours after it is sent, and any response need not be immediate.

Chat requires each user to have a computer connected to an electronic network. The network might be a local area network within a business, or it might be the Internet. Users also need a chat system, software that controls the connection between the computers of the people who are chatting. Many chat systems are free.

Chat is most commonly used for social interaction. For example, people might use chat to discuss topics of shared interest or to meet other people with similar interests. Businesses and educational institutions are increasingly using chat as well. Some companies hold large online chat meetings to tell employees about new business developments. Such meetings are particularly useful for companies whose employees are spread out geographically—companies with large sales forces, for example. Small workgroups within a company may use chat to coordinate their work. In education, teachers use chat to help students practice language skills and to provide mentoring to students. History students may chat with elders who lived through the period of history the students are studying. Science students may chat with professional scientists.

How Chat works?

There are many chat systems, including Internet Relay Chat (IRC), America Online (AOL) Chat, and Microsoft Chat. The different systems are very similar, but users can generally only chat with other people who are using the same system.

Each chat system may have thousands of users spread throughout hundreds of chat rooms. Chat rooms are a feature of the system’s software that allows people with similar interests to send messages to one another without receiving messages from all of the other people using the system. Chat rooms vary in topic and in level of conversation. Usually a chat room’s name describes the topic people in it are supposed to discuss.

Most chat systems have both predefined and user-created chat rooms. When people connect to a chat system, they can choose to participate in the rooms they find interesting or useful. Many systems have chat room operators who may remove people from the chat room if they do not obey the chat room's rules.

Chat rooms are usually dedicated to a particular group of people, such as teens, or to discussions limited to a single subject area, such as politics. Some chat rooms cover technical topics (computer programming languages or Web site design, for example), and others focus on aspects of popular culture (the television show Star Trek, for example). Chat rooms dedicated to topics such as computer trouble-shooting can be useful sources of information, because many people with expert knowledge enjoy helping others online.

Some chat systems provide special moderated chat rooms, particularly for chats with celebrities. A chat room may have hundreds of people talking at once. A moderator and a set of rules control who receives messages from whom in order to prevent a flood of messages flowing across people’s screens too fast to read. The moderator controls who may ask questions of the guest of honor. In some of these special chat rooms, participants are organized into virtual “rows,” as if they were in an auditorium. Users may chat freely with others in the same row, but not with people in other rows. Everyone in all rows hears the presentation given by the featured speakers on the “stage.”

Chat has its own jargon. People who chat commonly use abbreviations. BRB, for example, means "be right back." IMHO means "in my humble opinion."

FAX or Facsimile Transmission

Communication system that copies, sends, and receives documents by way of telephone lines. Also called faxing, this method of communication allows people to share exact copies of important papers by duplicating and sending them on one end, and then receiving and reproducing them on the other.

Fax Machine Facsimile (fax) transmission involves machines designed to transmit graphical information via normal telephone lines. After a special fax number is dialed and the phone connection established, documents are fed through the machine, which takes approximately one to six minutes to scan and convert the information into electrical impulses. The impulses are carried across phone lines and a receiving machine changes the impulses back to text, making a copy, or facsimile, of the document in the sending machine. Particularly in time-sensitive business transactions, fax communication has become a popular alternative to express mail because it is faster and generally less expensive. Sharp Electronics Corporation 

Facsimile machines came into use in the early 20th century when newspaper companies began using them to transmit photographs between branch offices. By the mid-1980s use of desktop facsimile machines had become commonplace for business and personal correspondence throughout the world. More recently, people have used personal computers to send and receive facsimile transmissions, or faxes, eliminating the need for a separate facsimile machine.

E-Mail

E-Mail, in computer science, abbreviation of the term electronic mail, method of transmitting data or text files from one computer to another over an intranet or the Internet. E-mail enables computer users to send messages and data quickly through a local area network or beyond through a nationwide or worldwide communication network. E-mail came into widespread use in the 1990s and has become a major development in business and personal communications.

E-mail users create and send messages from individual computers using commercial e-mail programs or mail-user agents (MUAs). Most of these programs have a text editor for composing messages. The user sends a message to one or more recipients by specifying destination addresses. When a user sends an e-mail message to several recipients at once, it is sometimes called broadcasting.

The address of an e-mail message includes the source and destination of the message. Different addressing conventions are used depending upon the e-mail destination. An interoffice message distributed over an intranet, or internal computer network, may have a simple scheme, such as the employee’s name, for the e-mail address. E-mail messages sent outside of an intranet are addressed according to the following convention: The first part of the address contains the user’s name, followed by the symbol @, the domain name, the institution’s or organization’s name, and finally the country name.

A typical e-mail address might be sally@abc.com. In this example sally is the user’s name, abc is the domain name—the specific company, organization, or institution that the e-mail message is sent to or from, and the suffix com indicates the type of organization that abc belongs to—com for commercial, org for organization, edu for educational, mil for military, and gov for governmental. An e-mail message that originates outside the United States or is sent from the United States to other countries has a supplementary suffix that indicates the country of origin or destination. Examples include uk for the United Kingdom, fr for France, and au for Australia.

E-mail data travels from the sender’s computer to a network tool called a message transfer agent (MTA) that, depending on the address, either delivers the message within that network of computers or sends it to another MTA for distribution over the Internet (see Network). The data file is eventually delivered to the private mailbox of the recipient, who retrieves and reads it using an e-mail program or MUA. The recipient may delete the message, store it, reply to it, or forward it to others.

Modems are important devices that have allowed for the use of e-mail beyond local area networks. Modems convert a computer’s binary language into an analog signal and transmit the signal over ordinary telephone lines. Modems may be used to send e-mail messages to any destination in the world that has modems and computers able to receive messages.

E-mail messages display technical information called headers and footers above and below the main message body. In part, headers and footers record the sender’s and recipient’s names and e-mail addresses, the times and dates of message transmission and receipt, and the subject of the message.

In addition to the plain text contained in the body of regular e-mail messages, an increasing number of e-mail programs allow the user to send separate files attached to e-mail transmissions. This allows the user to append large text- or graphics-based files to e-mail messages.

E-mail has had a great impact on the amount of information sent worldwide. It has become an important method of transmitting information previously relayed via regular mail, telephone, courier, fax, television, and radio.

Browser

Browser, in computer science, a program that enables a computer to locate, download, and display documents containing text, sound, video, graphics, animation, and photographs located on computer networks. The act of viewing and moving about between documents on computer networks is called browsing. Users browse through documents on open, public-access networks called internets, or on closed networks called intranets. The largest open network is the Internet, a worldwide computer network that provides access to sites on the World Wide Web (WWW, the Web).

Browsers allow users to access Web information by locating documents on remote computers that function as Web servers. A browser downloads information over phone lines to a user’s computer through the user’s modem and then displays the information on the computer. Most browsers can display a variety of text and graphics that may be integrated into such a document, including animation, audio and video. Examples of browsers are Netscape, Internet Explorer, and Mosaic, Opera. Browsers can create the illusion of traveling to an actual location in virtual space (hyperspace) where the document being viewed exists. This virtual location in hyperspace is referred to as a node, or a Web site. The process of virtual travel between Web sites is called navigating.

Documents on networks are called hypertext if the media is text only, or hypermedia if the media includes graphics as well as text. Every hypertext or hypermedia document on an internet has a unique address called a uniform resource locator (URL). Hypertext documents usually contain references to other URLs that appear in bold, underlined, or colored text. The user can connect to the site indicated by the URL by clicking on it. This use of a URL within a Web site is known as a hyperlink. When the user clicks on a hyperlink, the browser moves to this next server and downloads and displays the document targeted by the link. Using this method, browsers can rapidly take users back and forth between different sites.

Common features found in browsers include the ability to automatically designate a Web site to which the browser opens with each use, the option to create directories of favorite or useful Web sites, access to search engines (programs that permit the use of key words to locate information on the Internet, an internet or an intranet), and the ability to screen out certain types of information by blocking access to certain categories of sites.

A browser’s performance depends upon the speed and efficiency of the user’s computer, the type of modem being used, and the bandwidth of the data-transmission medium (the amount of information that can be transmitted per second). Low bandwidth results in slow movement of data between source and recipient, leading to longer transmission times for documents. Browsers may also have difficulty reaching a site during times of heavy traffic on the network or because of high use of the site.

The most commonly used browsers for the Web are available for free or for a small charge and can be downloaded from the Internet. Browsers have become one of the most important tools—ranking with e-mail—for computer network users. They have provided tens of millions of people with a gateway to information and communication through the Internet.