In less than 24 hours, Microsoft will start upgrading Windows 7 and Windows 8 machines to Windows 10. The software giant is preparing for this big release, at 12AM ET on July 29th (9PM PST on July 28th), by pre-loading the final version of Windows 10 on PCs eligible for the upgrade. A number of Windows 7 and Windows 8 users who have registered for the upgrade have started noticing that the full installer files for Windows 10 have been downloaded to C:\$windows.~BT as Microsoft gets ready for release.

Read next: Our Windows 10 review.

Microsoft will unlock and activate the Windows 10 install at midnight tonight, allowing some Windows 7 and Windows 8 users to upgrade. Not everyone will get access to the Windows 10 upgrade initially, though. Microsoft is rolling the upgrade out gradually to compatible systems, and the company is creating a queue to distribute the update in waves. Windows 10 testers have already been testing the final bits and they will be the first to receive a Day One patch that Microsoft is developing. The software maker has also been rolling out daily hotfixes to existing testers, fixing issues just days and hours before the final release.