Microsoft last week said the next Windows 10 feature upgrade will be available for all users to download and install sometime in late May - the third straight postponement for Windows 10. The decision illustrates the strain under which Microsoft's Windows-as-a-service model has been operating of late. What had been billed as a metronomic every-six-months release schedule for the feature-and-functionality upgrades has faltered, burdened by months-long delays.

Windows 10 1803 - last year's March upgrade in Microsoft's yymm format - launched about a month late. Microsoft claimed that the fall refresh, Windows 10 1809, was officially just one month behind but in reality 1809 was at least three months late. In both instances, Microsoft extended support so each received the promised 18 months of bug fixes.

The upcoming feature upgrade - designated "Windows 10 May 2019 Update" - will be released in "late May," Microsoft executive Mike Fortinsaid in an April 4 post to a company blog. The launch will also mark the start of the 18-month support span for 1903, the yymm identifier for the upgrade._

(As it's done before when deferring an upgrade, Microsoft has again retained a four-digit moniker at odds with the actual launch timeline.)

While Microsoft hasn't hewed to a specific day of the week for Windows 10 feature upgrades' releases, Computerworld selected May 21 - a Tuesday, the weekday Microsoft uses most often for updates of all types - as a likely target. Because Microsoft does like to end support on the first Tuesday of a month, a May 21 launch would mean a Dec. 8, 2020 retirement for 1903. (The span would then be 18 months plus 18 days.)

May 2019 Update, aka 1903

Why. Although Fortin implied that 1903 was prime time-ready - he called it "production quality" - the upgrade will slip from an expected April to late May so that Microsoft, users and company hardware partners can do additional testing. For the first time, Microsoft will use the "Release Preview" ring of the Windows Insider program to test an upgrade prior to its debut. (Microsoft used Release Preview last year with 1809, but only after it had been launched, then retracted.)

The six-to-seven weeks of further testing were an obvious reaction to the debacle of Windows 10 1809, which was issued with a known-but-yet-overlooked bug that destroyed user data. Microsoft does not want a repeat performance, or to be seen downplaying testing.

Support change. Because of the delayed launch, 1903 will probably be supported until Dec. 8, 2020, almost two months later than if it had debuted in April and patched until Oct. 13, 2020.

Impact. Users running Windows 10 1803 will have just five months of overlap with 1903, not the usual six. It's during those overlap months that someone interested in skipping a feature upgrade must act. Figure 1 shows the overlap.

IDG/Gregg Keizer Windows 10 1903's later-than-expected launch will shorten the overlap between it and 1803 to five months, giving users a month less time to migrate from the older upgrade to the latest code.

More important for commercial customers, the overlap between 1803 and for 1909, the months subsequent to Microsoft contending the latter is "business ready," will be a brief two months. (Computerworld pegged the delay between debut and "business ready" for 1909 at three months; it's difficult to believe that Microsoft will make the claim earlier, what with 1909's secondary job ... removing the bad taste of 1809's failures.)

On the other hand, users who end up with 1903 will have eight months, two more than the standard six, of overlap with the future Windows 10 2003, assuming that upgrade launches on time in April 2020.

October 2018 Update, aka 1809

Why. Seemingly rushed to release, 1809 was yanked from distribution just days after its Oct. 2, 2018 debut because of reports that the upgrade had mistakenly deleted user files. Rather than re-release the upgrade to the general public once the underlying bug had been quashed, Microsoft sent it back for testing through the Windows Insider program. Not until mid-January did the company resume automatic delivery and installation, and even then wisely opened the distribution throttle very slowly.

Support change. Microsoft adjusted support by just one month, pegging retirement for Home and Pro users at May 12, 2020.

Impact. By setting an end-of-support date without taking into account how 1809 actually rolled out, Microsoft short-changed users: Most Home and Pro customers who run 1809 will have only 16 months of fixes coming to them, not the standard 18.

April 2018 Update, aka 1803

Why. Various reports asserted that Microsoft postponed an anticipated April 10, 2018, launch for this feature upgrade because of a significant bug. (In hindsight, with the fiasco of 1809 in a rearview mirror, Microsoft clearly made the right decision with 1803.) By the time engineers had addressed the bug, April was over: Microsoft announced the release of 1809 on the month's last day.

Support change. Microsoft shifted end-of-support from October to November 2019 to account for the late launch.

Impact. Because Windows 10 1803 was preceded by on-time releases - both 1703 and 1709 launched on schedule if not before - the month-long delay had little impact on its own. As already described, it was only in combination with later launches, notably 1903, that 1803's postponement put some users in a pinch.