Microsoft picked a really odd number for the total machines on which Windows users can install their apps, but 81 makes sense when you realize Windows 8.1 is just around the corner.

This new limit means that the company made good on its Build 2013 promise to increase the roaming app ceiling that's currently cutting off Windows 8 users at just five devices.

"We heard growing feedback from many developers and from our most enthusiastic customers that the limit of five was not enough for their needs," wrote the Windows Apps Team in an official blog post today.

"Developers asked for more flexibility in implementing their business models, and customers wanted to run those apps on the variety of tablets, laptops and desktops they owned."

It'll be a win-win situation for both Windows app developers and users starting on Oct. 9.

Scratching the Surface

In addition to being just in time for the Windows 8.1 launch on Oct. 17, the new app roaming limit is also fit for the Oct. 22 release date of Surface 2 and Surface Pro 2.

Microsoft may be hoping that you'll upgrade to its new tablet, keep the old Surface around, and have a work PC, home desktop, laptop, and Windows Phone 8 smartphone to boot.

That would put a user just over the current five roaming app limit, and 81 would more than make enough headroom for owning all sorts of new Windows devices under one account.

By comparison, Apple sets its App Store limit to 10 total devices for one Apple ID. Microsoft is leaping over its rival and trying to make up for lost ground in the mobile territory.

Look for Microsoft to raise the roof starting Oct. 9.