1.3 Computer connectivity, the Internet and the Web

Expansion capabilities of a computer: slots, cards and bus

Most of computer components lay on a card of switch-plates called motherboard. However, we could need to connect other devices to motherboard in order that they can interact with processor and other components. That is realized through inserting an expansion card in one of I/O connectors of the motherboard.

An expansion card, when inserted, fits perpendicularly in a connector of the motherboard and has to be fixed by a screw on the opposite side. When computer is closed, we can be sure that the expansion card will remain well connected to the motherboard. Cards communicate each other and with other computer components through the so-called bus representing an internal computer network through which signals are transmitted from/to any computer part. Therefore, because of this connection system, any card inserted in a computer slot can communicate with other computer components, memory and microprocessor included. These slots, conceivable as bus connectors, offer a simple way for adding further equipment. In the original PC, bus used just 8-bit cards and could transfer about one million byte per second. As of now, a motherboard with a Pentium processor has a 32 PCI bit bus allowing transfer of 500 million byte per second. Obviously, a Pentium processor mounted on an 8-bit motherboard could not exploit most of its capacities. During the last years many types of bus have been designed, with different performances. Compatibility between buses and current cards is a critical topic.

1.3 Computer connectivity, the Internet and the Web

Communication ports

Optical Storage

External peripherals are connected to a computer through cables (or radio or infrared rays) using connectors called communication ports. There are many types, but the main ports are two: parallel and serial.

Parallel ports

Parallel ports or interfaces are so called because data transmitted between peripheral devices and central unit are sent byte by byte: the 8 bit of each byte are therefore sent in parallel (8 bit a time). Parallel ports are mainly used for connecting printer: for this reason every computer is equipped with a parallel port. There can be many parallel ports for connecting simultaneously a printer, a scanner, a backup device or a copy protection key (dongle).

Serial ports

Differently from parallel ones, serial ports do not transmit 8 bit a time, in parallel, but send bit by bit; i.e. one bit a time. Therefore 8 bit of a byte are sequentially sent, at a speed 8 times slower at least than a speed reachable by a parallel method. Serial ports are however more versatile and polyvalent, being used to connect PC to various types of peripherals, such as mouse, scanner, modem, external units.

1.3 Computer connectivity, the Internet and the Web

Internet

The Internet is a computer network made up of thousands of networks worldwide. There are organizations which develop technical aspects of this network and set standards for creating applications on it. All computers on the Internet communicate with one another using the Transmission Control Protocol/Internet Protocol suite (TCP/IP). Computers on the Internet use client/server architecture. This means that the remote server machine provides files and services to the user's local client machine. Software can be installed on a client computer to take advantage of the latest access technology.

An Internet user has access to a wide variety of services: electronic mail, file transfer, vast information resources, interest group membership, interactive collaboration, multimedia displays, real-time broadcasting, breaking news, shopping opportunities, and much more.

World Wide Web

The World Wide Web (WWW) is a system of Internet servers that supports hypertext to access several Internet protocols on a single interface. Almost every protocol type available on the Internet is accessible on the Web. This includes e-mail, FTP, Telnet, and Usenet News. In addition to these, the World Wide Web has its own protocol: HyperText Transfer Protocol, or HTTP.