From Mac Guides
MagSafe is the name used by Apple for the power connector first used in the MacBook Pro in 2006. The MagSafe was later introduced for use in the MacBook, although the MacBook Pro version supplies 85 Watts while the MacBook version only supplies 60 Watts. Therefore, a MacBook Pro MagSafe can be used with a MacBook, but a MacBook Magsafe adapter cannot be used with a MacBook Pro, as it will demand too much power from the adapter.
The connector is held magnetically, so that if it is accidentally tugged (for example, if tripped on), it comes out of the socket without damaging the computer. This is of benefit to both Apple, due to decreased support costs, and consumers, whose computers are less likely to face accidental damage.
While connecting it, the orientation of the power connector (top/bottom) does not matter. It also has an indicator light to show if it's charging.
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