Unlike Microsoft, Apple never puts its support lifecycle lengths in writing.
But while Microsoft revealed the Surface RT's lifecycle, it declined to spell out how long it will support Windows RT, the touch-enabled, tile-based OS that runs not only the Surface, but some tablets sold by other computer makers.
In a cryptic FAQ published on its support site, Microsoft said only, "Microsoft will make software updates, including security updates, available for Windows RT. Additional information regarding the Windows RT lifecycle policy will be communicated as available."
Supporting Windows RT -- as opposed to the Surface RT -- for less than 10 years would be a dramatic departure for Microsoft, and could raise the ire of customers, especially businesses that have adopted, or plan to, the mobile operating system.
For example, Windows 8, which Microsoft also launched Oct. 26, remains in Mainstream support until Jan. 9, 2018, and won't be fully retired until Jan. 10, 2023, when it exits Extended support.
To demarcate Windows RT's lifecycle as shorter than a decade would also rub against a move Microsoft made last February, when it quietly extended support for the consumer versions of Windows 7 and Windows Vista by five years, for a total of 10, to synchronize them with the lifespan of enterprise editions.
The lifecycle for Surface RT could be a harbinger of a shorter-than-usual support lifetime for Surface Pro, the not-yet-released tablet Microsoft plans to launch at the end of January 2013. That tablet will be powered by an Intel processor, and run Windows 8 Pro.