Former Windows chief Steven Sinofsky has revealed his perspective of being on the Windows team when Apple unveiled the iPad 10 years ago this week. Microsoft tried to make tablet PCs a thing with Windows XP, but the company didn’t get the timing, hardware, and software right in order to succeed. So when Apple unveiled its iPad in 2010, it surprised many people inside Microsoft.

Sinofsky admits that the iPad was “as much a challenge as magical,” especially as Microsoft had been “fixated on Win32 [desktop apps], pen, and more” over a period of 10 years. “The success of iPhone blinded us at Microsoft as to where Apple was heading,” reveals Sinofsky.

Microsoft had been anticipating a cheap, pen-based Mac to compete with the Windows-based Netbooks that were selling well. “Endless rumors of Apple’s tablet obviously meant a pen computer based on Mac. Why not? The industry chased this for 20 years. That was our context.”

Instead, Steve Jobs unveiled something that Apple described as a third category of device between a smartphone and a laptop, and it mocked the 40 million Netbooks that had been sold. Microsoft and its PC partners had been focused on Netbooks and cheap laptops. “We knew that Netbooks (and Atom) were really just a way to make use of the struggling efforts to make low-power, fanless, Intel chips for phones,” admits Sinofsky.

The iPad lacked a stylus, something that Microsoft had made central to its previous tablet efforts. “How could one input or be productive?” asks Sinofsky. “PC brains were so wedded to a keyboard, mouse, and pen alternative that the idea of being productive without those seemed fanciful.”

Apple’s biggest iPad challenge to Windows was the promise of 10 hours of battery life, something that was “unachievable in PCs struggling for 4 hours with their whirring fans,” admits Sinofsky. Apple also had the advantage of ARM-based processors, easy 3G connectivity, and a surprising $499 price point that directly challenged consumer laptops.

“The iPad and iPhone were soundly existential threats to Microsoft’s core platform business,” explains Sinofsky. “Without a platform Microsoft controlled that developers sought out, the soul of the company was ‘missing.’” The iPad clearly unnerved Microsoft and the Windows team, and Sinofsky reveals that knowing Apple’s tablet ran a full, robust OS “had massive implications for being the leading platform provider for computers.”

What Sinofsky doesn’t reveal is how, exactly, Microsoft responded to the iPad. Windows 8 was the response, an operating system that attempted to bring many of the clever user interface elements of Windows Phone over to laptops and PCs. While it worked relatively well on pure tablet devices, it confused laptop and PC users who weren’t used to the way Windows 8 worked.

Microsoft also responded to the iPad with its own tablet hardware, the Surface RT. Codenamed “Georgetown,” it was a secretive project that was a direct response to the iPad and the frustration of its PC partners failing to build a competitor. Microsoft kept it secret from its partners until the last minute, and it formed a new team internally to create its own tablet hardware with ARM-based processors inside. It was designed to bring Windows 8 to life and to launch alongside the new operating system.

Less than a month after launching Windows 8, Sinofsky left Microsoft following an executive shake-up and personality clashes within the ranks. Microsoft took a $900 million hit on the launch of the Surface RT six months later, simply because the company made too many Surface RT tablets that didn’t sell as well as it had hoped. Microsoft then spent the following years adjusting Windows 8 for PCs and laptops before walking back many of the iPad-chasing changes with Windows 10.