Microsoft on Thursday unveiled bigger-than-expected discounts for some buyers of its forthcoming Windows 7 operating system, as it sought to stoke up demand for new PCs and put the poor reputation of Windows Vista behind it.

In a few countries, including the US, UK and Japan, the group announced an aggressive limited-period offer, with the US price for the software’s most common consumer version set at $49.99, a 75 per cent discount to the list price. “Getting [Windows 7] out fast into people’s hands is important for them to shed the bad perceptions of Windows Vista,” said Michael Silver, an analyst at Gartner.