Credit: ZDNet

Ever since Microsoft recently began testing Windows 10 20H1 -- its Windows 10 feature update that isn't expected to start rolling out to mainstream users until April 2020 -- there's been lots of speculation about why Microsoft is doing this so early. Microsoft's Windows Insider team has made some vague references to some things being worked on requiring a longer lead time. But I'm hearing from my contacts the real reason is much more mundane: It's about aligning schedules between Azure and Windows engineering.



On February 14, Microsoft released a "Skip Ahead" Windows 10 test build that officials said was from the Windows 10 20H1 development branch. They did this even though Windows 10 19H1 still isn't done.



Some people wondered if this was a sign Microsoft might be moving to one Windows 10 feature update per year (nope). Others wondered if this was because of complexities around separating the Edge browser from Windows 10, as Microsoft is doing with its upcoming Chromium-based Edge release (also nope). And some others guessed the super-early 20H1 code drop was related to Windows Lite, the rumored version of Windows that looks nothing like Windows (still nope, I hear).



Instead, here's what my sources say is happening.



It's taken about a year, but the impact of last spring's big Windows reorg which resulted in Windows engineering moving to the Azure team, is starting to manifest. Azure has been using a customized version of Windows 10 Server as the core of the Azure platform for quite some time. But the team behind the Windows core OS -- which (confusingly) is not the same thing as WCOS -- hasn't really prioritized Azure up until now. Instead, it's been prioritizing the needs of Windows client, Server and Xbox.



This is starting to change. Beginning with the next major update to Windows core, which is the guts of Windows (meaning the kernel, file system, networking stack and such), the Azure team at last will be using the most-up-to-date version of Windows core instead of a much older version, my sources. say. Moving forward, the Windows core features the Azure team wants will get top billing.



On the client side of the house, Microsoft will continue to roll out two new feature updates of Windows 10 per year around April and October, as it does currently. These feature updates will be built on top of the Windows core platform release that the engineering team delivers internally only. These internal platform releases go to various Microsoft teams (Windows client, Server, Xbox and Azure) twice yearly -- in June and December.



The Windows team is close to finalizing Windows 10 19H1. If schedules had all aligned, the core OS team would already be well on its way to finishing the new core platform release (codenamed "Vanadium"), targeted for internal delivery by June 2019, which would be the base of the next Windows 10 release. But the timing just doesn't work out. As a result, my contacts say, the new plan is for the core OS team to skip its internal June platform release and just focus on the December 2019 internal release (codenamed "Vibranium") -- which will be the basis for the Windows 10 20H1 release.



Still following along? Yes, it's complicated.



The 19H1 Windows 10 feature update coming this April is built on top of the December 2018 core OS platform release. The Windows 10 19H2 feature release won't be built on the (non-existent) June 2019 platform update. Instead, Microsoft's plan is to build 19H2 on top of 19H1 by adding some patches and features, and to back-port some of the 20H1 platform features to 19H2, my contacts say. Because the Windows client team is sticking to two feature releases a year, it has to do this kind of fancy footwork to deliver a Fall 2019 release. This 19H2 release might appear like a more minor update, but only to those paying close attention.



Does this mean Microsoft is going to move to a major/minor schedule with Windows 10 feature releases moving forward? I hear the answer is no. This year is just a messy one-off, sources of mine say.



Microsoft's plan remains to continue to roll out two new Windows 10 feature updates every year (over the howls of protest of many business and consumer users). If all the stars align,the 20H1 release will be built on the Windows 10 core OS Vibranium platform which engineering will deliver internally to various Microsoft teams as of December 2019. If all goes as planned, the Windows 10 20H2 release will be built on the Windows 10 core OS platform delivered internally in June 2020 (which is codenamed "Manganese").



Here's hoping the realigned schedule will deliver at least some trickle-down improvements in the stability and consistency of the Windows core OS platform across Windows client, server and Xbox. Meanwhile, Windows Core OS (WCOS) work -- which initially was incubated by the Windows core OS team -- moves forward for brand-new devices, such as Centaurus, Pegasus, Surface Hub 2, HoloLens 2 and more.

Update (March 6): As one reader pointed out, if Microsoft does stick with this new Skip Ahead model, the fall update would become more like a Cumulative Update with a few new (and possibly optional) features back-ported from the next year's spring release. So -- in a way -- the spring Windows 10 feature update would have, effectively, 36 months of support (six months or so before they are delivered as the guts of the fall release, and then 30 months of additional support, as currently offered by Microsoft). My head hurts.