WatchOS

watchOS is a series of mobile operating systems developed by Apple for their Apple Watch platform. It is based on codebase of iOS.

watchOS 1 through watchOS 8 was 32- and 64-bit compatible. However, watchOS 9 dropped support for 32-bit software. watchOS 9 is also the first version of watchOS to support only 64-bit software. watchOS 5 was the first version of watchOS to bring 64-bit support.