Ballmer was speaking at the D: All Things Digital conference in Los Angeles, where the day before Apple chief executive Steve Jobs said PCs running the Windows operating system are in decline.

Jobs said Windows computers would decline in popularity as people used other means to connect to the internet, consume content and work.

Ballmer said although Windows could become more customized, the bulk of the market will remain multipurpose.

"I think people are going to be using PCs in greater numbers in years to come, but I think PCs will start to look different", he said.

"Nothing that people do on PCs today will get less relevant. There is no question that what people do on a PC they will do on other devices", said Ballmer

He said it is unlikely that there is going to be a single device that will do everything.

"I think there will be general-purpose and specific devices. The PC will continue", said Ballmer.

Asked whether he was using the term PC to envelope things that people do not think of PCs, including the iPad, he said "of course".

"I see our competition trying to eliminate products that have not been popular and pushing a new product that might be more popular", said Ballmer.

There will be a range of devices, there will be different looks. Some people will want the comfort of Windows and some might want it to be more customized, he said.

"We are very well suited with what we have today. We see opportunities coming up ahead. It is going to be competitive. There is going to be a lot of competition around form factors", said Ballmer.

This article was first published by Computer Weekly