Here's a rundown of what's new for Windows 10 PC users and Windows 10 Insider testers on the PC and mobile fronts, in terms of new 'Threshold' and 'Redstone' builds. By Mary Jo Foley for All About Microsoft | March 10, 2016 -- 18:31 GMT (10:31 PST) So far this week, Microsoft has released three different Windows 10 builds to its various constituencies. On March 10, Microsoft rolled out a new "Redstone" Windows 10 Mobile test build -- No. 14283 -- to Windows Insiders on the Fast Ring. This build goes to devices that originally shipped with Windows 10 only, namely Lumia 950, 950 XL, 650, 550, Xiaomi Mi4 and Alcatel OneTouch Fierce. (Other Windows Phones will start being able to get Fast Ring builds once Microsoft finally upgrades them from 8.1 to Windows 10 Mobile, something expected by many of us to finally start to happen this month.) Build 14283 includes improvements to the Phone app and updates to Outlook Mail and Calendar apps. There's also a new Feedback Hub welcome dialog, though it won't be until the next Mobile and PC builds that Microsoft actually brings together the Insider Hub and Windows Feedback apps into a single new app called the Feedback Hub. There are also various fixes and a couple of known issues, including a sync issue for those who have paired Microsoft Band 1 or 2 to their phones. The blog post on the release has all the details. Earlier this week, Microsoft also released a new Cumulative Update for Windows 10 users running PCs with Windows 10 1511 (the November Threshold 2) update. That new Cumulative Update, known both as KB 3140768 and Build 10586.164, includes bug fixes and improvements only, rather than any brand-new features. Among the updates in 10586.164 for PCs are improved Bluetooth support; improved app-installation reliability; a handful of security fixes; and more. Microsoft also pushed the version number of its latest Windows 10 Mobile Threshold update to 10586.164. This build is almost identitcal to last week's 10586.122, Microsoft officials admit. Last week's Windows 10 Mobile 10586.122 was for Windows Insiders in the Slow and new even slower (Release Preview) rings. This week's 10586.164 was also for Insiders on the Slow and Release Preview rings, plus those with retail open market devices.The only real differences between 10586.122 and 10586.164 for mobile is a couple of bug fixes, along with some updates to get the update to run on retail devices.