What is the difference between Game Mode on a SDTV and on a HDTV?,do they both perform the same,what are the differences with them?,if there is any?.I have a SDTV and it has Game Mode and its off and I'm not sure if I need to use it?.

Generally you sacrifice a bit of quality to make sure you are seeing the quickest possible picture. Usually means skipping any filters, etc. the tv might normally run a picture through.

If you aren't noticing lag in your games, you probably don't need it on. If you end playing games with meters that depends on perfect timing or some fighters, you might want to turn it on.

Just from a general observation standpoint with my Samsung LNT5271F; for testing purposes I set the picture mode to the default normal factory setting. When game mode is enabled the contrast is increased to 90 from 80, 120Hz is set to Low, and the detailed mode is locked out.

Though from messing around with the detailed settings it would seem like when the game mode is enabled the black level adjust and dynamic contrast are set to medium; the audio settings are set to custom and locks out all subset options when audio is selected.

Yes, there are really two different meanings for the term "Game Mode", depending on the manufacturer and TV:

A) Game mode being a picture setting, where contrast and edge enhancement are often increased and other settings are locked to certain values. Sort of an attempt to "make the picture pop" by the manufacturer, although sometimes this actually makes everything look worse.

B) Game mode being a processing setting, where game mode skips various image enhancement steps to try and reduce display processing lag. Can result in a slightly worse image, but reduces the "everything has already happened" effect, particularly when using non-native display resolutions.

I also have a 71F. Game Mode reverts the TV to 60hz. Therefore eliminating AMP, and any 120hz benefits.