Windows fans, take note: Microsoft is about to hit an important milestone in the run-up to the release of Windows 10 at the end of the month: Numerous reports have pegged this Thursday as the day the company will wrap work on Windows 10 and declare the OS is ready for "release to manufacturing" (RTM).\nRTM is a development marker that signifies the Windows 10 code is officially stable enough to distribute to OEMs (original equipment manufacturers). That gives them just three weeks to pre-load the OS onto new devices prior to sale, but it should allow at least some manufacturers to get Windows 10 machines onto the market -- and into users' hands -- as back-to-school sales commence.\nSeveral sources cited this week for the RTM release, including The Verge and Neowin, which pointed to "internal sources" at Microsoft.\nHere's more on how close Windows 10 is to completion:\n\nA recently-leaked edition, build 10163, offered strong hints that July 9 is, indeed, the correct date for RTM. Windows leaker WZor noted that build 10163 included a reference in the Calendar app to July 9, as the "RTM Sign-Off."\nBuildFeed pointed out that the same Windows 10 build was tagged as from "th1," which is seen as a reference to the internal RTM branch of "Threshold," an earlier code name for the OS. (Another th1 build -- 10176 -- was released Sunday, according to BuildFeed.)\nThe latest official build -- 10162 -- was released to testers last Thursday -- the third build issued in a week, another sign that the company is fast closing in on final code.\n\nFor OEMs, the narrow window of availability means they'll have to scramble to get Windows 10 on their hardware. In the past, they've had months: For Windows 8, they had 12 weeks between the time Microsoft declared its code RTM and the first sales of Windows 8 devices and for Windows 7, there was a 13-week gap.\nThe manufacturers most likely to have machines ready by month's end are those that sell build-to-order PCs through online outlets. Among them, Dell plans to ship pre-ordered Windows 10 systems on July 29.\nWith reports by Gregg Keizer at Computerworld.