Summary:Beginning this summer, Microsoft will offer free Windows 10 upgrades to hundreds of millions of PCs. A recent Windows Update contains details about how the Get Windows 10 (GWX) program will work. By Ed Bott for The Ed Bott Report | April 20, 2015 -- 17:55 GMT (10:55 PDT) What was already an open secret has now been confirmed (apparently accidentally) by one of Microsoft's partners in the PC supply chain. Thanks to offhand remarks from AMD's president and CEO Lisa Su, we now know that Microsoft is planning to launch Windows 10 at the end of July. (Previously, Microsoft had only committed to "this summer" as a launch date.) But what will actually happen when the appointed date rolls around? That poses some interesting logistical questions for Microsoft. The Windows 10 upgrade program is going to be one of the largest software delivery projects in history. Microsoft is offering full, free upgrades for every PC currently running Windows 7 or Windows 8.1 Service Pack 1 (excluding those running Enterprise editions, which don't qualify for the free upgrade). That means a 2GB+ upgrade package downloaded to each PC. So just how big is the eligible Windows 10 upgrade base? It is certainly measured in the hundreds of millions, representing PCs running Windows in 111 languages and 190 countries worldwide. Apple's been doing this for a few years with OS X, but on a much smaller scale, measured in the low tens of millions for each new release. Microsoft's upgrade program for Windows 8.1 was probably larger than that but still only a small fraction of the worldwide PC installed base. There's actually a road map hidden in plain sight, included with a recent optional update for Windows 7 and Windows 8.1. An XML file installed with that update contains important clues about a program called GWX: Get Windows 10. KB3035583 describes itself innocuously enough: "This update enables additional capabilities for Windows Update notifications when new updates are available to the user. It applies to a computer that is running Windows 8.1 or Windows 7 Service Pack 1 (SP1)." That's it. No, seriously, that's the entire description. But the KB article does go on to describe the files included with this update, most of them containing the acronym GWX. And as the file details make clear, GWX is short for Get Windows 10. The update also sets up four scheduled tasks, one of which runs an "appraiser" app that checks prerequisites for the download and subsequent upgrade. And in the GWX folder is an XML file that contains a roadmap of the different phases in store after that update is installed. The first salvo is the "Anticipation UX." A pop-up advertisement in one of three predefined sizes will appear, presumably saying something like "Windows 10 is coming. Get excited!" The next phase is labeled the Reservation Page. I suspect that's an opt-in page, where someone seeing this sequence of ads can read about the process and then say yes, they're ready to upgrade. The phases after that are mechanical: Upgrading, Download In Progress, Download Complete, Ready for Setup, Setup in Progress, Setup Complete. The whole process is similar to the flow of events that members of the Windows Insider program are already familiar with: opting into an update that enables delivery of the upgrade files, which are downloaded in the background and then installed with minimal user intervention. I've seen a handful of people trying to spin this update process as a sneaky move on Microsoft's part, but I have a hard time seeing this as adware. It is, instead, perfectly targeted advertising, offering a free upgrade to a product currently running on the system where the ad is being displayed. There are no hidden costs (aside from those incurred by the download itself) and the upgrade isn't going to be installed without your explicit consent. It can't, because there's at least one license agreement (and probably several) you're going to have to click through. And don't forget that KB3035583 is still an Optional update for Windows 7 (it's listed as Recommended for Windows 8.1). Novices don't typically venture into the Optional Updates section, so Windows 7 users won't see any advertisements for Windows 10 until Microsoft moves that update to the Recommended category. Also note that this update is not being offered to Enterprise editions or on domain-joined machines. So here's how the rollout is likely to go: Windows Insiders will get a Preview build that will become the Current Branch. Think of this as the replacement for what would previously have been a Release Candidate. The Anticipation campaign, with on-screen ads for anyone who installed the Optional KB3035583 update, will probably begin around the same time as that build goes out to members of the Insider program. That should be in late June or early July. Upgrades then begin rolling out in late July and early August, staggered to reduce the load. And as the population of upgraded PCs grows larger, a new feature in Windows 10 will kick in, reducing the load on Microsoft's servers and potentially making upgrades much faster on local networks. Options in Windows 10 will allow peer-to-peer transfers of apps and OS updates, on the same network and potentially over the Internet. Of course, while this public release is rolling out slowly, over a period of several months, Microsoft will continue to deliver new feature updates. We already know that the new unified OneDrive sync client is likely to appear after the official release of Windows 10. There will probably be several of these minor feature updates between this summer's Windows 10 launch and the rollout of the first big feature update a year later, code-named Redstone. The Project Spartan browser, new Mail and Calendar apps, and anything else delivered through the Windows Store can also be updated on their own schedule, independent of the rest of Windows. When all is said and done, Microsoft will be supporting Windows 10 users in four separate rings: Insider Fast and Insider Slow will continue to get early access to updates; the Current Branch will be the public release channel; and a new Current Branch for Business will allow businesses to delay feature updates by several months, so that they can minimize the risk that a flawed update will have an impact on business processes. The big question is how many consumers and small businesses will say yes to the free Windows 10 upgrade, and how quickly. Several recent data points suggest that close to nine in 10 PCs running Windows 8 have updated to Windows 8.1. Getting Windows 7 holdouts to upgrade might not be as easy a sell.