Yes, it will work on Mac OSx.
Yes, as long as your iMac has Mac OS9 or higher.
Apple have, essentially, two types of computers - the iMac series and the Pro. The pro is aimed more at business use with the iMac more for the consumer (although, obviously, there is some overlap).
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Both are good, but the i mac has more features, a huge screen and they give you a magic mouse and a mac keyboard. While the mac mini is a hard drive and can turn any PC into a mac and it is cheaper but slower. So, it is your choice.
No, they both use the exact same operating system. You will see no difference in performance on either. Just depends on which suits your needs.
With fingers.
no
You can't use mods on Mac or iMac, it only works on PC.
No Macintosh has included a floppy drive since the release of the iMac G3 in 1998. If you need to use a floppy disk, you will have to purchase an external USB drive.
Get the one that suits your needs. For portability get a MacBook Pro or MacBook Air. For a desktop and large screen, get the iMac. If you have a nice computer monitor, check out the Mac Mini. It is a real computer that is very small.
You can plug up your 2012 iMac when you are finished using it. Nothing will happen to the iMac. After the iMac is fully charged, make sure to unplug it.
When running and not in sleep mode the 21.5" iMac uses 205 watts of power. The 27" iMac uses 310 watts. In sleep mode they each use around 2 watts.