A network is a connected (via some form of cables) system of computer hardware. The Birkbeck College Department of Crystallography has a local network which consists of all electronically connected computers within the department. Such a network is called a Local Area Network (LAN). Other LANs within the College might include those of the Chemistry, Biology, Physics, English, German (and so on !) departments.
Some of Birkbecks computers are at a different location within the city ; however, they are still connected to each other and hence also constitute a LAN. When several such LANs are connected to each other (over wider distances) we refer to the ensuing structure as a Wide Area Network (WAN) !
The Internet is the world-wide conglomerate of LANs and WANS, ethernet links and dedicated phone lines, a network of networks. The Internet spans political and geographical borders and through connectivity of all manner of computers it provides information on a wealth of topics, from apple pie over atomic decay to zeta particles !
The Crystallography department is itself connected to the Internet which is how you can actually access our computers - and read this file !

Internet Addresses

Computers on the Internet can be accessed by specifiying their address. This can be done in two ways:
  1. Using the Internet Protocol (IP) address. This consists of four numbers separated by a full stops (the dotted quad), and is known as the IP Number, for example

  2. Using the Domain Name System (DNS):. The DNS Address consists of letters (sometimes containing a numerical digit or two) and there are not necessarily four parts to the address as with the IP Number.

    For example denotes the VAX computer called mv3b in the crystallography department at Birkbeck College in the Academic Community in the United Kingdom !

You can probably see that the DNS address is more user-friendly than IP numbers. DNS addresses are hierarchical and its often possible to guess addresses based on abbreviations and country codes. For example: