Apple’s Wireless Keyboard, Generation 3, was released in October 2009 and was a slight revision to the Generation 2 version. The Generation 3 version used only two AA batteries (instead of three) and became Apple’s new standard, shipping with iMac computers released the same day.
Like its Generation 2 predecessor, this keyboard was thin and had an aluminum enclosure with thin white keys, similar to the laptops of the time. In addition, functions were added to the function keys such as media controls. Its round power button was found on the right side of the keyboard—opposite the cylindrical battery enclosure. It connected via Bluetooth.
This keyboard style was updated one more time to a Generation 4 version when Mac OS X Lion (10.7) was released. The Generation 4 version updated two function keys: the Exposé key was changed to a Mission Control key, and the Dashboard key changed to a Launchpad key.
This keyboard design was replaced entirely on October 13, 2015, with the Apple Magic Keyboard.
Source: Wikipedia