With about six months left on Microsoft's free Windows 10 upgrade promotion, Redmond is stepping up its efforts to get Windows 7 and Windows 8.1 users to upgrade to its newest operating system.

Windows Update has three classes of update: important, recommended, and optional. The first category is always downloaded and (if preferred) installed automatically. The last category always requires manual downloading and installation. The middle, "recommended," is by default treated the same as "important," but users can also opt to treat it as equivalent to "optional."

As announced last October, the free Windows 10 update has been promoted from an "optional" update to being a "recommended" one. This means that with the default Windows Update settings, the new operating system will be downloaded automatically, and its installer will be started.

The operating system will not actually install itself unattended; Microsoft says that users will be able to reject the upgrade or reschedule it for a time that's more convenient. The company has also described a variety of registry settings that suppress the upgrade.

In common with most Windows Update deployments, the change from "optional" to "recommended" will be phased in, so Windows 7 and 8.1 users may not see the change immediately.