Retail sales of Windows 7 were well over 200% higher than Vista's in the two operating system's first days of being on sale in the States, the NPD Group has revealed.

But although Windows 7 software unit sales were 234% higher than Vista's, it seems revenue growth wasn't as strong, said to be due primarily to discounts.

"Microsoft's program of early low-cost pre-sales, high visibility marketing, and aggressive deals helped make the Windows 7 software launch successful", said Stephen Baker, vice president of industry analysis at NPD.

"In a slow environment for packaged software Windows 7 brought a large number of customers into the software aisles".

Perhaps a result of the different economic climate as Microsoft has launched this latest OS, compared to when Vista was launched, it seems PC hardware sales were down.

Windows PC sales were down 6% compared to PC sales during the Vista launch week.