Larson-Green and Angiulo appeared on stage to demonstrate a Windows 8 machine upgraded with Windows 7 devices.
Microsoft announced the grand opening of its Windows online store, modeled after Apple's iTunes store. It will sell apps and content for Windows machines.
The store will be open in 231 markets around the world. (Companies typically restrict sales to specific markets, as some content may not be available worldwide because of copyright issues and local laws. A launch in that many markets at once is unusual.)
There are plenty of third-party apps available for iPads, iPhones and devices running Google's Android system. Sinofsky acknowledged that Microsoft's app store will likely be slim at first.
"We know some people might count apps and look for their favorite apps," he said. Hinting at more to come, he added, "We see today as a grand opening."
He said there are hundreds of apps added every day, in 109 languages. He said the Windows store has more apps than any other app store had at its opening.
Sinofsky said there have been 1,000 PCs certified for Windows 8, with the cheapest costing about $300. There will also be new models of slim, lightweight laptops called ultrabooks.
He reiterated that Windows 8 is designed to work equally well with touch-screen computers and those using keyboard and mouse commands.
Sinofsky opened by talking about past versions of Windows. He noted that the current version, Windows 7, came out three years ago this week. He said 670 million Windows 7 licenses have been sold since then.
He said that in creating Windows 8, "We shunned the incremental. We boldly reimagined Windows." He said there have been 16 million installations of preview versions of Windows 8.
The software will go on sale at midnight local time around the world.