Bill Gates has demonstrated a range of concept devices developed by design-school students, including a tablet form factor and ones with catchy names, such as Yummy Kitchen Connect, which was a small screen that attaches to a refrigerator.

Speaking at the Windows Hardware Engineering Conference (WinHEC), Gates also said Microsoft would develop natural-language interfaces, such as speech, that would show up on a range of devices.

"When you scale down the size of things, the need to complement keyboard input becomes increasingly important."

He said the future would also be marked by advances in unified communication.

"The phone is going to be the PC, and the PC is going to be the phone," Gates said.

He also said software plus services, what Microsoft calls the ‘Live Era’, would also be critical to deliver data and services so a user's information could follow them around.

Gates also revealed Windows Vista sales figures, and christened Windows Server 2008 at WinHEC.