Starting late next year, you’ll have a choice between Windows 10 and Windows 10 as the operating system if you want to buy a new PC.
Microsoft is ending sales of PCs pre-installed with Windows 7 Professional and Windows 8.1 on October 31, 2016. Normally, Microsoft stops sales of the previous version of Windows two years after the release of a new one, but since Windows 8 proved to be pretty unpopular, they extended the life for an extra two years.
This has no effect on security support for Windows 7 and 8.1. Both will be supported for 10 years from the time of general release. Windows 7 until January 2020 and Windows 8 until January of 2023.