The original version of Windows 10 (also retroactively named version 1507 and codenamed "Threshold 1") was released in July 2015. It carries the build number 10.0.10240; while Microsoft has stated that there was no designated release to manufacturing (RTM) build of Windows 10, build 10240 was described as an RTM build by various media outlets. It was retroactively named "version 1507" by Microsoft per its naming conventions that have the last 2 digits of the year and the month number for future stable releases of the operating system.
