Windows has always had its own versioning conventions: historically it was a one-digit major and a two-digit minor, so windows 2.1 was 2.10 in full (its predece

Windows has always had its own versioning conventions: historically it was a one-digit major and a two-digit minor, so windows 2.1 was 2.10 in full (its predecessor was 2.03, and it was followed by 2.11), and NT 3.5 was followed by NT 3.51. This scheme was moved away from with Windows 10, which switched to a year/month versioning scheme (so the first W10 update was version 1511, as it was released in November 2015), then to the current "halves" system.