The days of the PC are numbered, says IBM's Chief Technology Office.

According to Dr Mark Dean, who worked on the 5150 - the first IBM personal computer - PCs will continue to be much-used devices but they're no longer at the leading edge of computing

"They're going the way of the vacuum tube, typewriter, vinyl records, CRT and incandescent light bulbs," he said in a blog written to mark the 30th anniversary of the 5150, which was launched on August 12, 1981.

"PCs are being replaced at the centre of computing not by another type of device - though there's plenty of excitement about smart phones and tablets—but by new ideas about the role that computing can play in progress."

Dean said it's becoming clear that innovation flourishes best "not on devices but in the social spaces between them, where people and ideas meet and interact".

"It is there that computing can have the most powerful impact on economy, society and people's lives."

Dean admitted that he too has moved beyond the PC, with a tablet PC as his primary computer.

"When I helped design the PC, I didn't think I'd live long enough to witness its decline," he said.

"I'm proud that I was one of a dozen IBM engineers who designed the first machine."

However, Frank Shaw from Microsoft said in another blog the world was not looking towards a post-PC era and instead should embrace the "PC-plus era" since 400 million PCs are expected to be sold this year.