The Windows 10 RTM (release to manufacturing) milestone is close at hand.

On July 13, Microsoft temporarily suspended availability of Windows 10 for PC preview builds in preparation for the upgrade process, which commences July 29.

"Windows Insiders have been the first to see our work on Windows 10 at every stage. Now you will also be the first to get a build flighted to you using the channels that we'll use for targeting and deploying to PCs for our staged rollout," said Gabe Aul, head of the Windows 10 Insider program in a July 13 update to a previous blog post.

More from Aul:

"We're suspending the availability of Windows 10 builds briefly while we prepare for that (rollout), and the next build that we flight to you will be delivered using the production channels. Starting tomorrow (July 14), we will also not be delivering any additional ISOs at this point as we really need Insiders to be using, stressing, and validating our distribution and upgrade processes. We'll make ISOs available again in the future, but for now we ask you to upgrade your current build via Windows Update once the next build is released."

Microsoft is planning a staggered -- and I'd say "soft" -- Windows 10 launch starting July 29. It's not going to be the typical big-bang Windows launch.

July 29 is the date when Microsoft will start rolling out Windows 10 to its Windows Insiders in the form of a new build flight. Others who have "reserved" their copies of Windows 10 as part of Microsoft's first-year-free upgrade promotion will get the RTM bits over the following few weeks.

Microsoft will continue its Windows 10 Insider program after the product RTMs. The Windows team will continue to offer Insiders preview builds and to offer those with the final RTM bits regular, ongoing feature and security updates via Windows Update.

Later this fall (possibly in October, according to sources), Microsoft is planning to deliver a larger-than-usual update to Windows 10 for PCs to those who have the RTM bits installed on their machines, sources have said. Around this time is when I'd expect to see the majority of new PCs and tablets optimized for Windows 10.

Trivia for Windows Insiders: Why is there a red shirt and shorts pinned to the wall in the photo Aul tweeted over the weekend of himself and Distinguished Engineer Don Box? (Box, by the way, also is Director of Development for Silicon, Graphics and Media in the Windows group.)

One day, in the Shiproom, (Microsoft Distinguished Engineer) Mike Fortin came in with red shorts and a red T-shirt, Box tweeted. "From then on, when anyone brings in an embarrassing bug (or -- gasp -- a regression), they must wear red.

(And for those wondering, the new red shirt has nothing to do with the red shirts worn regularly by Microsoft Cloud & Enterprise Chief Scott Guthrie, Box was quick to note.)

"And no, I have yet to wear a red shirt, but we have a few days left before we are done," Box tweeted on July 12.