(Telecompaper) Microsoft announced it will start offering its Windows software free to manufacturers of mobile phones and tablets with screens of less than nine inches. Announced at its Build conference for developers in San Francisco, the end of a royalty on the software is expected to encourage more companies to develop Windows devices, especially lower-cost models. Also at the conference, Microsoft introduced Windows Phone 8.1, the latest version of the mobile OS. It features the digital assistant Cortana, based on a character from the game Halo and powered by the Bing search engine. Cortana gets to know the user over time from his or her's phone behaviour in order to serve up relevant content and features. Microsoft also added the Action Center, to manage new activities and notifications in one place; and Senses, a panel to monitor data use, storage space and battery life. Businesses also get new control features such as simplified device enrollment, a built-in mobile device management client, S/MIME for encrypted mail and VPN support. Nokia was the first to announce new phones running Windows Phone 8.1, and the upgrade will roll out to current Windows Phone 8 users over the coming months. Microsoft also announced an update to its PC operating system, Windows 8.1 Update, which rolls out in the coming week to existing customers.