Microsoft said at the Windows 10 launch event that the company would be releasing the updated operating system in the summer of 2015. Thanks to a note by Kevin Turner at the Credit Suisse Technology Conference, we have a slightly more specific timeline. 

Turner said in the note that the company will be releasing Windows 10 in "late summer and early fall." The language is a bit peculiar and we have posted the comment below. The thing I want to tell you about on Windows 10 is in the Windows 10 timeframe, which we plan to talk about the end-user consumer experiences in the early spring, we'll have a developer preview and be able to talk to that in depth in the early summer timeframe. And then by next late summer and early fall we'll be able to bring out this particular OS. That's the current plan of record.