Early-bird Windows 10 testers won't be getting new preview builds of the operating system for the time being because the company has stopped deliveries to focus on distribution issues.\nMicrosoft now says it's "very close" to finishing up work on the operating system, which makes sense -- it's set to arrive on July 29, two weeks from tomorrow.\n"We're suspending the availability of Windows 10 builds briefly while we prepare for [the official roll-out process], and the next build that we flight to you will be delivered using the production channels," Gabriel Aul, engineering general manager for Microsoft's OS group, wrote yesterday in an updated blog. "...We're working very hard to get everything just right."\nAul said the suspension will be short-lived, but noted that disk images used by testers for a "clean" install of Windows 10 will also be deferred. He urged testers to concentrate on "using, stressing, and validating our distribution and upgrade processes."\nHere's what the latest move means for Windows 10 preview users:\n\nPre-release activation keys will no longer validate earlier preview builds shipped as .iso files. Aul did not say whether activation codes will be provided down the road for those who hope to test Windows 10 after the official launch and want to perform a fresh install rather than an in-place upgrade from Windows 7 or 8.1.\nThe build and .iso suspensions mean Microsoft will soon declare Windows 10 at the "release to manufacturing" (RTM) milestone. At that point, the OS code will be passed along to device makers for pre-loading on new hardware.\nInsider participants will get the final OS code on July 29, but Microsoft doesn't plan to allow others to upgrade that day. Instead, it will stagger the free upgrades it's promised to Windows 7 and Windows 8.1 users, triggering the update on PCs that have been checked for compatibility after the OS have been silently downloaded. (Eligible users can "reserve" a copy of Windows 10 via the notification campaign they've been getting since last month.)\n\nAlthough a Microsoft official said Monday that no Windows 10-powered PCs would be available for sale on the July 29, Microsoft later reversed itself, saying that OEMs (original equipment manufacturers) including Dell, Acer, Hewlett-Packard and Lenovo, would begin selling Windows 10 devices that day.\nWith reports by Gregg Keizer at Computerworld.