During the outage, the site displayed a message that said, "Due to the eagerly anticipated Windows 7 pre-order offer, we're experiencing a higher level of demand on our website than usual. This means you can't access the site right now and we're sorry about that."

The store was briefly back online at 11 a.m. ET, but an hour later it had again gone down.

According to a report by the BBC, Amazon's UK store claimed that it had moved more copies of Windows 7 in the sale's first eight hours than it did in the 17-week run of a similar pre-order offer in 2006 for Windows Vista.

The sale, a repeat of the U.S. pre-order deals that ended last Saturday, kicked off today when Microsoft offered heavy discounts on Windows 7 Home Premium and Windows 7 Professional in the U.K., France and Germany. The discounts are good through Aug. 14, or until supplies last.