Microsoft Windows Insider head Dona Sarkar Microsoft In September 2014, Microsoft did something very uncharacteristic: Not only did it introduce the new Windows 10 operating system — it invited people to try out the extremely unfinished operating system, a full year and a half before it would hit store shelves.

This program, dubbed Windows Insider, was the brainchild of Bill Karagounis and Gabe Aul, both long-time Microsoft engineers.

Over the past two decades, Windows has been developed in a near-total vacuum. Only Microsoft employees saw the new version in the works until it was almost ready to hit store shelves — "We would go for years before we would show our product to the world," Karagounis tells Business Insider.

In early 2014, recognizing that Windows 10 was a major inflection point for the company under new CEO Satya Nadella, the pair went to Windows boss Terry Myerson and his executive team. This time, they suggested, Windows users should "come along for the journey" with product engineering, Karagounis says.

By September 2015, 7 million people had signed up with the program; there are over 10 million Windows Insiders today, across Windows 10 PCs, tablets, and smartphones. About a year ago, Aul stepped down from his role as leader of Windows Insider to focus on his product duties, making way for fellow Windows veteran Dona Sarkar to take over.

Gabe Aul and Dona Sarkar "fight" over the "big red button," the fan-favorite way that Aul would release a new version of Windows 10 to Insiders. Gabe Aul

Now, as Microsoft prepares to release the Windows 10 Creators Update, a major free upgrade coming on April 11th, Sarkar says that the Insider program is playing a key role in the future of the operating system. The motto within Windows Insider, Sarkar tells us, is that these power users are "the millions who represent the billions."

"[Windows Insider] is actually changing the way we build and change Windows," Sarkar says.

'More than a beta testing program'

Apple and Google both make beta versions of their operating system available to app developers, ahead of official major upgrades for the masses. Karagounis says that Windows Insider is different.

"Some people have beta testing programs," Karagounis says. "We have more than a beta testing program; we have a whole community."

The way Windows Insider works is simple: Go to the Windows Insider website with your PC or tablet and sign up, though Microsoft suggests not using any computer you'll have to use every day, just in case a new build of Windows breaks things. Then, in your Windows 10 settings, you'll be able to choose the "fast ring" or the "slow ring." Microsoft Director of Program Management Bill Karagounis Microsoft

On the fast ring, Sarkar says, you'll get a new version of Windows mere days after the Microsoft team finishes it and it goes through some basic testing. On the slow ring, you'll get something a little more stable, a little less frequently. Either way, it's speedier than waiting a year or two between major Windows releases.

"Now, technically, we release Windows every week," says Sarkar.

Sarkar refers to the practice of running Windows Insider as "Insidering," and it revolves around the Feedback Hub app. It's become a community unto itself, Sarkar says, with Insiders offering "lovely, really detailed" suggestions on everything from the opacity of the Start menu, to the placement of the "Save" button in the new Paint 3D app.

'Because that's what you should do'

Sarkar says that Microsoft has totally revamped its engineering culture around the Windows Insider program: She met with a bunch of Windows product managers recently, she said, and every single one of them told her that they were holding off on making more decisions until more Insider feedback comes in.

And it's a two-way street, Sarkar says. Every team within the larger Windows organization now has a "community champion" — a Microsoft engineer, given a mandate to work with the Insider community on a specific topic, based on their knowledge and interests, from gaming to programming to the Windows Store app market.

For example, Sarkar says, a visually impaired Windows programmer is working with Insiders as one of those "community champions," to gather feedback on Windows 10's accessibility features and bring it back to the team.

Windows 10 is going after people who aren't historically big computer users. Darren Weaver/Business Insider

"We try to mirror our Insider community with our community within," says Sarkar. "Because that's what you should do."

To Sarkar's mind, this approach is especially important now, with the Windows 10 Creators Update. Past versions of Windows have focused on a very straightforward computer experience, basically for people who sit down and type. With new apps like Paint 3D, and new stylus features to go with it, Microsoft is courting creative and artistic types.

"This is an update for people who aren't like Windows engineers," Sarkar says.

'The biggest fans of Windows I've ever seen in my whole life'

The Windows Insider model has been enough of a success that it's being emulated across the rest of Microsoft. Office Insider and Xbox Insider both launched recently, giving similar levels of pre-release access to dedicated fans.

Windows Insider itself just this past week expanded into letting corporate customers into the program, so they can give their own brand of feedback on the future of Windows 10. The goal, Sarkar says, is to just keep talking to Windows users and hear what they have to say.

This level of openness has won the Windows Insider team a certain level of celebrity within the Microsoft fan community, around the globe. Now, when Sarkar wants to tease a new build of Windows 10 coming down the pipeline, she hides the version number in a photo on her Twitter account, as kind of game with Insiders.

Like so:

Windows Insider fans even created their own mascot, the "ninjacat," which Microsoft has readily adopted as the officially-sanctioned mascot of Windows 10, at least amongst employees.

The Windows Insider Ninjacat mascot. Microsoft

All in all, Sarkar says, it's a level of enthusiasm for Microsoft and Windows that she's never felt before, but that she's more than ready to accept, even as the ranks of the Windows Insiders continue to grow.

"I tell everyone, I've been waiting around 12 years for this," Sarkar says. "These are the biggest fans of Windows I've ever seen in my whole life."

Karagounis is no less excited, but a little more muted: "I probably had more modest plans for the program," he says.