But the new competitors aren't due out until late this year and early next year, giving Apple a huge headstart which it has already capitalised on by selling two million iPads in about two months. Apple also recently surpassed Microsoft in market value to become the world's biggest tech company.
Ballmer admitted he had "a lot of work to do" to catch up with iPad but said the "race is on" to see who could dominate the new segment. Ironically, Microsoft was first to spruik tablets but they didn't gain any traction.
He did not believe the shift in software to the internet "cloud" was a major threat to Microsoft, just a time of transition.
"Depending on what you're trying to get done with the device at different times, there will be people who absolutely will want the comfortable and familiar look of Windows," said Ballmer.
"There's nothing bad for us in the trend. We are moving from a world that's fundamentally good for us to a world that could be even better."
Ballmer took a shot at Google, ridiculing it for peddling two different operating systems - Android and Chome. He then conceded the Microsoft also had multiple operating systems.
He said the face of the PC would continue to morph with multiple different flavours - some with keyboards, some without, others pocket-sized and touch-based - and Microsoft would have its hands in as many pies as it could.
People would continue to have multiple devices and use each one differently, but nothing that people are doing on a PC today was going to get less relevant tomorrow.
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