What is the greatest British invention of all time? The steam engine, electric motor, the television? Each of these has made an enormous impact on our everyday lives, but nothing has had quite the same instant global impact as the web.

The internet set about changing things almost immediately ... for everyone. Businesses depend on it, communication networks are built on it, and thousands of terabytes of vital information are shared over it every day.

The word 'revolution' is bandied about perhaps a little too often these days, but there are few words strong enough to describe the effect that the internet has had on our world, and the relative speed with which it has made itself indispensable.

Curiously, the origins of such a monumental invention are a little difficult to pin down. When we think of the birth of flight, we remember the Wright Brothers, while the discovery of the theory of evolution is attributed to Charles Darwin.

But what about the web? Well, many people would probably name Tim Berners-Lee - recently knighted and still more directly involved in the development of the web than he originally planned.

But even Sir Tim points out in his book, Weaving the Web, that much of the hard work had already been done before he even showed up. And, although everyone remembers his groundbreaking work, there are plenty of others whose crucial contributions are already being forgotten.

Definitions
What exactly is the world wide web? This is not the dumb question it first appears - the average web user will probably find it fairly hard to define exactly what the web is, how it works or what it does. Even Tim Berners-Lee paints it in somewhat vague terms as "an abstract space of information".

This, however, is the way it was intended. When we turn on the TV, most of us have no idea how many elements, both in and out of the box, come together to produce the picture we see - all that matters is that it works. So it is with the web. It brings you the information you seek, while hiding how it does so extremely effectively.

In the simplest terms possible, the web is a vast collection of data files and resources, coded in its own Hypertext Mark-up Language (HTML) and transferred using Hypertext Transfer Protocol (the 'http' that's mentioned at the start of most web addresses). When you click on a link, your client (or browser) accesses the web server (host computer) where that page is stored, but to reach you the data has to ride the complex series of gateways, nodes and addresses that make up the internet.

The web as we know it today is a much more user-friendly version of a network that has been in operation for decades. Before the web, you needed a degree in computing to do almost anything online - now you can start clicking and trust your mouse to guide you. That's why it's so hard to define and so easy to use.

The web today
By current estimates, the internet contains at least four billion pages of information, pumped out by around 50 million hosts to nearly a billion users worldwide. It has created massive new brands (Amazon and eBay to name but two), and the net shows no signs of slowing down.

Could the web ever sprawl out of control? It's a difficult beast to tame but, although it's largely left to its own devices, there are web watchdogs of a sort; laws controlling what you can and cannot do online (although enforcing them is a different matter), and bold new initiatives to wipe out some of the most obvious problems.

Only recenntly Bill Gates vowed to eradicate spam within two years, although how much this will cost the consumer remains to be seen. And, at the very top of the tree, the World Wide Web Consortium (W3C) has been around since 1995, examining ways it could run better and faster. Fittingly, it is here that you can still find the web's creator.

Nevertheless, some might argue that the net has turned out nothing like Tim Berners-Lee originally intended. For something that was meant to be a free, global databank, unrestrained by big business, large parts of it are now devoted to sleaze, while much of the respectable bits are being tamed by corporate forces intent on using the web as another in a long line of marketing tools and a way of generating more profit.

So how did it get this way? Let's delve back into the past to find out.

The internet: the early years
The science of computing began well over a century ago, but took off in the 1940s, primarily for defence and intelligence purposes. Telecoms, meanwhile, has roots dating back to the mid-19th century and was more about sharing than concealing information. It was only when these two technologies got together that anything resembling a world wide web could happen - and this took a lot longer than you might imagine.

From the 1960s the US government, in partnership with some key universities, began exploring the potential of networking computers. There were half a dozen of these networks by the late 70s, all talking to different users and often in deliberately different languages. After all, what was the value in making something like Arpanet - designed to protect Western intelligence against a Soviet nuclear strike - available to the wider world?

It took people with vision, prepared to work hard for almost no reward, to change these attitudes.

One example of this is Project Gutenberg, the brainchild of a computer operator named Michael Hart, who decided in 1971 that the best use of Xerox's million-dollar mainframe was not to do number-crunching for its clients, but to type in the US Declaration of Independence and make it available to anyone who wanted it.

To its credit, Xerox not only accepted the argument but the project is still around today, publishing a new e-book daily, totally free of charge. It typifies the new attitude to knowledge that developed as the Cold War ended.

But there were technical obstacles, too. The only way the networks of the 1970s could communicate with each other on a wider scale was if someone devised a new language capable of talking to them all. And in 1979 someone did - a key breakthrough that Berners-Lee himself stresses: "If you are looking for fathers of the internet, try Vint Cerf and Bob Khan who defined the 'Internet Protocol' (IP) by which packets are sent on from one computer to another until they reach their destination."

Thanks to Cerf and Kahn, by 1983 the internet - the global network itself - was up and running, after which the big ideas came thick and fast. In the mid 1980s the University of Minnesota started a text-based information server known as Gopher, while File Transfer Protocol (FTP), the forerunner of today's peer-to-peer culture, arrived just a few months before a chap called Tim Berners-Lee uploaded data to the very first web server in August 1991. At the time, few were hailing it as a revolution.

"I didn't find lots of people willing to get excited about the idea of the web," recalls Berners-Lee. "They quite reasonably asked to know why it was different from past, or other hypertext systems."

But different it most certainly was - in effect, this was the moment that the web was born. All in all, the transition from the internet to the web as we know it today took place in the decade from 1982-1992.

Unfortunately, not even the web's biggest fans can claim it has been an unmitigated success. Yes, it has given us access to billions of pages of information and a 24/7 digital culture, but it has also given us unfortunate side effects, such as cyberstalking and grooming, and has become an effective platform for viruses, hackers, scammers and spam.

And although it has provided business with profitable new opportunities, it also created expensive new headaches. Cybersquatters and hackers need to be prevented, while online piracy threatens to eat into profits, and consumers face mounting problems with credit card fraud and identity theft.

And the influence of the web must not be underestimated. A recent report by the National Children's Society, for example, suggests that what certain people see and do online might directly affect how they behave in the real world. We are only beginning to learn what its true long-term effects might be.

Whatever next?
Most people will admit that the world is a much better place with the web than without it. And the beauty of it is that the web is constantly evolving. New applications arrive all the time, and new technologies help to make them run faster and better.

Where once there was only one 'language of the web' (namely HTML), now there are Java, Shockwave and XML. Similarly, where once there was only email, now we have quicker ways of communicating, such as instant messaging and P2P.

So despite its problems, the web is, thankfully, here to stay ... at least until something better comes along. Scarily, at current growth levels there are apparently only enough URLs (unique web addresses) to last us until just past 2050. But with billions now invested in making the web work, there is little enthusiasm to reinvent the wheel and do it all over again.

But by then the highly adaptable web will have undoubtedly evolved to cope.

History of the internet: 1812-present

History of the internet: Sir Tim Berners-Lee

History of the internet: Unsung heroes