Previous Macintosh operating systems (versions of the classic Mac OS) were named using Arabic numerals, as with Mac OS 8 and Mac OS 9.[22][20] Until macOS 11 Big Sur, all versions of the operating system were given version numbers of the form 10.x, with this going from 10.0 up until 10.15; starting with macOS 11 Big Sur, Apple switched to numbering major releases with numbers that increase by 1 with every major release.