Gnarls Barkley's song 'Crazy' made chart history last weekend, by becoming the first song ever to reach number one in the UK charts, based on sales from computer downloads alone.
The song entered the charts at number one last week despite the fact that the single will only be released in shops today.
Downloads from Internet websites have been included in the UK charts since last April, after traditional single sales fell to extremely low levels.
Download sales of a single can now be counted a week before the track is released in shops, according to new rules.
Gennaro Castaldo of HMV said: "It does represent chart history in the making. It shows the download market has really taken off."