Mark Shuttleworth, who created a version of Linux software named Ubuntu, said Dell is happy with the demand it has seen for Linux PCs that were introduced in May.

Dell, the world's second-largest PC maker after Hewlett-Packard Co, now offers three consumer PCs that run Ubuntu Linux.

She added that Dell was pleased with customer response to its Linux PCs. She said Dell believed the bulk of the machines were sold to open-source software enthusiasts, while some first-time Linux users have purchased them as well.

Open-source software refers to computer programs, generally available over the Internet at no cost, that users can download, modify and redistribute.

The Linux operating system is seen as the biggest threat to Microsoft's Windows operating system.

There are dozens of versions of Linux, available for all sorts of computers from PCs to mainframes and tiny mobile devices.