Microsoft is increasing the number of Windows 8 and 8.1 devices on which users can install Windows Store apps from 5 to 81. (And no, that's not a typo.)

The new app-roaming limit takes effect on October 9 and applies to Windows Store/Metro Style apps associated with a single Microsoft account, according to a new Microsoft "Windows App Builder" blog post on September 27.

Microsoft officials told developers attending its Build conference in June that the company was planning to make a change to the 5-device limit, based on feedback.

"Developers that decide to have the app enforce a constraint around the number of devices must disclose that constraint to Windows Store customers and set expectations appropriately," according to the new blog post.

I'm not exactly sure why the new limit is 81. (I mean that particular number; I'm not questioning whether 81 is sufficient.) I've got a question in to Microsoft about that.