Windows 10 is an operating system of the Windows NT family developed by the American company Microsoft. Officially presented on September 30, 2014, it has been publicly available since July 29, 2015. Although the system is called Windows 10, it is version NT 6.4 for versions up to the “Technical Preview”, the first Windows NT version 6 was Windows Vista. Windows 10 remains an ultimate version of Windows NT 6.0; nevertheless since the final version it does carry the internal number 10 instead of 6.4. It is the successor to Windows 8.1. The paid upgrade to Windows 10 is possible for any device with Windows 7 and Windows 8.1. This upgrade is possible from the GWX.exe application (icon at the bottom right of the taskbar), by ISO via the Media Creation Tool, or by using the tools dedicated to assistive technologies. After the upgrade, the device stays on Windows 10 indefinitely, attaching the product key in BIOS or UEFI from version 10240, and attaching it to a Microsoft account from version 14393 .