Mine use to work perfectly and now stopped. Tried saving in settings again...uffta! :b. Still doesn't work.
What is GM?
It stands for "Gold Master" aka the final production version of a software/firmware. This is identical to the final or the 1st (general) public release. You may have heard of software "going gold" meaning a final build of the code has been selected and finalized, designated to be released to the public. Microsoft uses the synonymous term "RTM" or "release to manufacture".
Code progression typically goes:
Alpha, beta, RC (release candidate) which there can be several of (RC1, RC2)? then once they hit a point where they feel a RC version is free of any show stopper bugs, and is stable and fit for public release, an release candidate officially becomes the final release.
Gold, final, production, RTM, GP (general public) and on and on.