Microsoft released Windows 10 to the masses on Wednesday, giving the world an opportunity to update to its newest operating system.

Users of Windows 7 and Windows 8.1 who “reserved” a free update through the Get Windows 10 app will start to see a notification pop-up informing them that their update is ready for installation. The update is going out in waves, which means it’s likely that some users won’t actually get it today. In addition, the installer will check to make sure that a device’s apps and hardware are compatible with Windows 10, and will warn the user before proceeding or avoid installing altogether.

People who already have the latest pre-release build of Windows 10 installed won’t see another major update. Build 10240, which Microsoft released to members of the Windows Insider Program two weeks ago, is the same build that people who are upgrading from previous versions of the operating system will receive Wednesday. Terry Myerson, Microsoft’s head of operating systems and devices, said in a blog post announcing the roll-out that those people who already have the operating system installed should check to make sure that they have the latest patches applied.

As part of the roll-out, the company also opened up its Media Creation Tool for Windows 10. With the tool, people who use Windows 7, Windows 8 and Windows 10 can create USB disks and ISO disk images that can be used to install Windows 10 on other computers. People on platforms that can’t use the Media Creation Tool such as Windows XP and Mac OS X will get direct links to ISO downloads so they can also create installation media.

The upgrade is free for Windows 7 and 8.1 users from Wednesday until July 29, 2016. After that, Microsoft will charge everyone to upgrade their older systems. People who are on an older version of Windows are ineligible for a free upgrade, so they’ll have to pay right out of the gate.

While creating installation media will allow users to perform a clean installation, Microsoft has stressed that users won’t get Windows 10 for free unless they upgrade their qualified system first. After that, they’ll be able to successfully wipe the contents of their computer and re-install the operating system either using Windows 10’s built-in reset functionality or by installing cleanly from a disk.

Microsoft also released an evaluation version of Windows 10 enterprise that IT professionals can try out for free to check out the operating system’s features. It’s worth noting that edition is not meant for consumer use. People who download it have to register their information with Microsoft, agree to be contacted by Microsoft during the 90-day preview period and agree that they’ll have to do a clean install of their operating system if they want to downgrade from Windows 10.

As with all operating systems, it’s entirely likely that some users will encounter bugs with Windows 10 when it’s first installed. (Some people are having problems even getting the operating system to install in the first place.) Those folks who want to ensure that their PC keeps working perfectly will likely want to hold off from upgrading on launch day and wait a little while until the dust settles.