Windows 10 will arrive July 29th, but that doesn't necessarily mean everyone will be ready to go on day one. Case in point: A Lenovo representative told Windows Central that the company will take orders for PCs with Windows 10 preinstalled on launch day, but that those machines won't ship until about mid-August.
Why the delay? Look no further than Redmond. Microsoft released Windows 10 to PC makers (the so-called "RTM" or "released to manufacturing" build) later than it normally does, which seems to have some PC makers scrambling. A Microsoft rep went on record to say to expect Windows 10 PCs "very soon after" launch, but not on launch day itself.
Despite Microsoft's statement, however, both HP and Dell say that they'll have Windows 10 machines ready for launch. In HP's case, you can order a Windows 10 PC through HP.com now and have it arrive on launch day, with PCs arriving at "select" retailers beginning August 2nd.
Dell will begin selling Windows 10 PCs on the 29th through its website, and if you opt for next-day shipping, you could have your new Windows 10 PC as early as July 30th.
The story behind the story: In past years, Windows launches have been highly coordinated affairs: PC makers would normally get the final RTM build several weeks in advance of the official release, so they would have time to install the new OS onto their new PCs in time for launch day. This time around, the RTM has come relatively late in the process. Build 10240, which was previously reported to be the RTM build, didn't arrive until last week.
But Microsoft has changed its approach to Windows releases starting with Windows 10, and that apparently means a change to back-end procedures, too. However, the fact that Windows 10 will be free for all users of Windows 7 and 8.1 softens the blow some, and makes any delay on PCs with Windows 10 preinstalled easier to stomach.