Clearly many are confused.
If my Lumia 1520 was on fast and got both .96 and .107 (both) being of the 10586.xx (non Redstone) heritage it makes no sense that I switch to slow to get the latest 10586.164
I've always understood the Redstone builds with the funky numbers are for current phones shipping with 10 and that to get the it requires Insider set to slow, but then what do they get on fast?
The Insider app itself could go deeper with scenarios when picking.
This should help alot explaining it more thoroughly .....
Fast Ring:
This is the most advanced and risky ring or release channel of Windows 10 Insider Preview. If you use this ring to download and install new Windows 10 Insider Preview builds, get ready to face random issues and bugs as the builds released to this ring will be very new and less tested. Whenever Microsoft puts new features or fixes issues in Windows 10 builds, the company releases the build first to Fast ring. You are not supposed to use Windows 10 Insider Preview build downloaded from Fast ring as primary OS as it may crash and can cause issues. If you are a geek and want to test latest features of Windows 10 without waiting, you can join this ring.
Slow Ring:
This ring or release channel is less risky than Fast ring. When a new Windows 10 Insider Preview build is released to Fast ring and tested by Insiders for a few days or months, Microsoft releases the same build to Slow ring so you get a thoroughly tested build of Windows 10 on this ring. But again the build is a testing build, so you can still get bugs and issues on this ring. If you want to try and test new features of Windows 10 but want to take less risk and can wait for some days or months, then you can join Slow ring.
Release Preview Ring:
Release Preview ring or release channel is the least risky ring of Windows 10 Insider Preview. Microsoft will not release latest testing builds to this ring. Users on this ring will get the current public build but they will receive cumulative updates and newer apps in advance which will be released later to public in coming days or months. So if you want to stay on safer side but want to receive early updates and apps, you can join this ring. But don't expect latest testing builds on this ring which are delivered to Fast and Slow rings.
Now when we have talked about different rings or release channels of Windows 10 Insider Preview builds, now lets understand different branches or Windows 10 development:
Microsoft has divided Windows 10 development and release schedule into 2 main branches:
◦Development Branch
◦Current Branch
Development Branch:
Development branch contains the testing builds of Windows 10 which are delivered to Fast and Slow rings. These builds contain new features and improvements but might also come with bugs and issues. If you are on Fast or Slow rings, you get Windows 10 builds from Development branch. At the time of writing this article (i.e. Feb 11, 2016) the build on Development branch is build 14257 which is also known as Windows 10 Redstone build.
Current Branch:
Current branch contains Windows 10 build which is the latest build released to public. For example, at the moment the latest public build of Windows 10 is build 10586. So the current branch contains Windows 10 build 10586 at the moment. When Microsoft will release a new build to public, the same build will be considered the build of Current Branch. If you are on "Release Preview" ring, you are a part of Current Branch and you'll get early cumulative updates which will be later released to public. When a new update is released to the build on Current branch, the build number is incremented by decimals such as build 10586.104, etc.
So now you should have no doubts or confusions about different branches and flighting rings or release channels of Windows 10:
◦Development Branch - Fast ring and Slow ring
◦Current Branch - Release Preview ring and Public builds
If you want to test latest features of Windows 10 and are ready to get issues or bugs, you should use Fast or Slow rings to get builds from Development branch.
If you want to use Windows 10 as primary OS and don't want to face issues or bugs, you can either use "Release Preview" ring of Windows 10 Insider Preview or use the publicly released build of Windows 10. Both builds will be released from Current branch.
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