1080p/24 came with the 1.8 update, the problem was that there are quite a few TVs that can display it, but haven't got the right EDID information to tell the PS3 that they can. As the only options were 'Auto' (where it checks with the TV if it can play it) and 'Off' these TVs couldn't display 24fps from the PS3 if connected directly to it (most notable the Samsung M86/7 and the Toshiba X series had this problem to varying degrees). The 1.9 firmware adds an option to force 24fps mode on.
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To be pedantic...
1080p/24 came with the 1.8 update, the problem was that there are quite a few TVs that can display it, but haven't got the right EDID information to tell the PS3 that they can. As the only options were 'Auto' (where it checks with the TV if it can play it) and 'Off' these TVs couldn't display 24fps from the PS3 if connected directly to it (most notable the Samsung M86/7 and the Toshiba X series had this problem to varying degrees). The 1.9 firmware adds an option to force 24fps mode on.