THEIR exact locations are not widely publicised, for pretty obvious reasons. The majority of them are on US soil, with a handful overseas, albeit on territory controlled by the US Department of Defense. They are the 13 computers on which the entire internet is based.

These 13 machines hold what is called the root zone file, the starting point for all addresses on the web. This is the list of where to look for an internet address, directing the searcher towards another machine which holds the rest of the address. Without these machines, pretty much nothing on the internet would work.

It is this baker's dozen which lies behind an international dispute pitting the United States against the rest of the world. It is a dispute coming to a head at an international summit in Tunisia starting today, and which has, or so some claim, the potential to end in the collapse of the internet altogether.

At issue is the role of the Internet Corporation for Assigned Names and Numbers (Icann). Inasmuch as the global free-for-all that is the internet has a governing body, then Icann is it. Set up by the US Department of Commerce in 1998, Icann is a private company which oversees the core domains, the internet's address book.

Icann decides who gets the top-level domains, .com, .org and .net, as well as the country codes, .uk, .us etc. It is also responsible for allocating space on the internet.

It was due to become independent from the US government next September, but earlier this year the US announced it would be retaining its role as the ultimate authority for the internet. This prompted opposition from other countries, who argued that no one country should be in the position of final arbiter of the web.

To try and find a compromise, the EU proposed setting up an international body to be in overall charge, but while this has found favour with critics of the existing system, with China, Brazil and Iran foremost among them, it has so far been roundly rejected by the US, raising the prospect of a stalemate at this week's summit.

According to Viviane Reding, IT commissioner for the EU, without agreement some countries could start running their own versions of the web. One of the internet's main strengths, its ability to cross national boundaries, would then be in jeopardy.

"We have to have a platform where leaders of the world can express their thoughts about the internet. If they have the impression that the internet is dominated by one nation and it does not belong to all the nations then the end result could be that the internet falls apart," she says.

While this may be the doomsday scenario, there is no doubt that important issues are at stake, according to David Eagle, principal lecturer in computing at Teesside University. He says the degree to which the internet can be controlled may be limited - once a domain name has been issued there is little regulation over what goes on a particular website - but the key consideration is commercial.

This is particularly relevant to emerging economies, where the growth of their web-based business may be hampered by charges for domain names, proportionally greater than for more developed countries. Coupled with the need to create more space on the internet, Mr Eagle says this provides a compelling argument for shifting control away from the US.

"If we're going to create more domain names, shouldn't we have a more democratically accountable organisation that does that?", he says. "It wouldn't be a problem if the internet hadn't grown as quickly as it has, but in the emerging economies it is getting more difficult to allocate addresses."

He says that although the argument seems to be about laws and regulations, at heart it is about business, and the ability of one government to provide a commercial advantage to its businesses. An international body to oversee the internet would remove this temptation.

And although in the short-term the outcome of the tussle will make little difference to most internet users, it is of long-term importance in deciding how the web will develop.

"It is placing the internet as a global resource, rather than an American resource. I don't think any one government should have control of that resource," he says. "Wresting control, even if it is nominal control, would be a very significant step. It is more healthy for the growth of the world to not have that handled by one jurisdiction."

But supporters of the status quo point to the light touch the US government has exercised in its jurisdiction over Icann. Although the US, under pressure from the religious right, earlier this year vetoed a plan to set up a new .xxx domain for pornography, this was a rare example of interference. Instead, they argue, handing control over to an international body would actually increase the possibility of politicians trying to dictate what goes on the web.

"There are people who think they can do it better, and like the idea of having power over the most important piece of communications infrastructure on the planet," says Chris Green, technology editor of Computing magazine. And the US has good reason for refusing to budge.

"Fundamentally, the internet is an American invention. The founding network was the creation of the US Department of Defense and it still belongs to them," he says.

He dismisses talk of the collapse of the web as politicians' grandstanding, and says even if some countries pulled the plug, one of the internet's strengths is its ability to find another route to a destination. He believes the Tunisia conference will prove to be little more than a talking shop. "The internet will still be a free for all," he says.

"The hardware and infrastructure still belongs to the US, but they recognise that it has grown far beyond something that any one country can control or enforce."