50 million copies will be installed in Europe by 2010 analysts predict
The latest version of Microsoft's flagship operating system, Windows 7, is available for pre-order in the UK.
Amazon said that sales of Windows 7 in the first eight hours it was available outstripped those of Windows Vista's entire 17 week pre-order period.
The home version of the operating system costs around £50, while the professional version costs around £100.
The limited number of pre-ordered copies will be shipped on 22 October, the same day it goes on sale in stores.
Pre-orders are available from a number of retailers, with the period ending on 9 August.
Analysts IDC predict that some 177 million copies of the operating system will be in place by the end of 2010, 50 million of which will be in Europe. The firm estimates that products and services surrounding Windows 7 will generate $320bn (£195bn).
The software requires a "clean install", meaning that prior versions of Windows will have to be removed before Windows 7 can be installed.
Because of a recent European Commission anti-trust ruling, Windows 7's European version will not be integrated with Windows' Internet Explorer, meaning that a browser will have to be installed separately.
"Both Windows 7 upgrade packages shot to the top of the Amazon.com software bestsellers chart over in the US as soon as they were made available for pre-order at the end of June," said Chris Poad, software director at Amazon UK.
"With the significant discount currently on offer, a similar level of high demand was expected in the UK for what is undoubtedly the biggest software release for many years."