(This column appears in the January 06 issue of PC Advisor)

Back in the summer of 2003, more than a quarter (26 percent) of the people who responded to our online poll didn't know what OEM was, and a further 32 percent said they didn't understand what the terms of the licence were. I imagine the situation is still about the same, but to a lot of people those three letters mean big savings.

OEM stands for original equipment manufacturer, and in this context is used to describe software (and some hardware) that is supplied to Microsoft-licensed computer manufacturers - it's a ‘trade' version, which is cheaper than the retail variety, and comes without Microsoft support. The company that makes or assembles the computer is responsible for providing Windows support to its customers.

It's a pretty good deal from Microsoft's point of view; lots of OEM sales means fewer support calls to the Microsoft helpdesk. The company's original intention was that OEM Windows would be available only to system builders via authorised distributors, and everyone gained. It didn't quite work out like that, however.

Now, out of the blue, there's a change of attitude. OEM software may only be sold if it's preinstalled on a new computer that's supplied by a system builder.

At a stroke, Microsoft has yanked the rug from beneath an army of freelance system builders - some of them doing it to earn a crust, and some of them for their own satisfaction - who must now buy the full retail version of Windows XP, which is currently priced at a shade under £250, rather than the OEM version, for about £92.

I've asked Microsoft to explain why it's suddenly altered course, but so far the company hasn't come up with an answer. I suspect it has come under pressure from many of the smaller system-building firms, who saw the freelance builder as a threat to their sales. I certainly can't think of any other good reason, and neither can many of our online forum members, who have been pretty outspoken about it.