One thing I wasn't expecting, from last month's new Apple hardware announcements, was the new MagSafe 2 power connector. The new Retina MacBook Pro, along with the 2012 "Ivy Bridge" MacBook Airs, have a new MagSafe port, physically incompatible with the previous generation, unless you use a little adaptor widget, which was luckily introduced for sale on the very same day.
MagSafe is Apple's name for their clever system of attaching the power line to their laptops to charge. Some say too clever by half. The cable has two pins, arranged as two symmetrical pairs , so you don't need to worry about orientation when you connect it up. The pins live in a little oblong recess, surrounded by a thicker shiny metal lip, which is magnetized. The power socket has the complementary inverse shape and magnet, meaning that they eagerly cup together to form a snug charging connection when introduced. The other significant benefit of this arrangement is the ease of disconnection, nice in itself, with the additional blessing that if some clumsy person, perhaps a passing dalmatian, blunders through your cable while you're tethered to the mains, your computer doesn't fly from the desk and shatter, the magnet just snaps free. I'm a big fan.
And so, on to MagSafe 2. Essentially it's the same thing, but in a different shape. The pin configuration and spacing seems to be the same, but the magnetic lozenge, and the companion socket have been reshaped to be longer in the lateral plane, and slightly shorter in height. The shape of the connecting plug has returned a the symmetrical rectangular nub, with embedded charge indicator. Reminiscent of the first generations of MagSafe, but Aluminium, rather than white plastic, and slightly longer, making it perhaps a bit more finger friendly.
Most commentary I've seen about this form change has settled on the Retina MacBook Pro as the motivation for this change, speculating that the move to thinner unibody laptops requires a thinner connector. I'm pretty unconvinced by that argument. The MagSafe 2 is only a millimetre or so thinner than the previous design. I think that if your design constraint was to shrink the connector, you could make it smaller. Furthermore, the traditional Magsafe port is almost the same height as a USB or HDMI socket, and the Retina laptop case houses these ports, without compromise. I have a different theory about the reasoning behind this new shape.
I think the most significant change is that the contact area of the magnetic surface has now nearly doubled. It's a lot more grippy than it's ancestor. Anecdotally, over the lifespan of the MagSafe, I've heard complaints from other users about the reliability of the chargers, particularly about cable and connector failure. Having never experienced similar problems with the half-dozen plus MagSafe chargers I've owned, I've puzzled about this. I wonder how many people might be disconnecting their chargers by yanking on the cable. This works as a method of disconnection, but it's not a very sensible approach, it puts a lot of mechanical stress on the junction between the cable and the plug. Do it enough, and you'll eventually break it. The magnetic coupling is most efficient in the horizontal plane. What you ought to do is flick the plug out, by hooking a finger underneath the connector plug, and angling it up away from the socket.
Apple certainly seemed to recognise that there was a UI problem here. Perhaps an expensive one, if enough customers were returning broken chargers to stores. They even produced a technote about the correct way to disconnect a MagSafe. Then MagSafe plug connectors changed shape over time. The strain relief on the cable junction lengthened, and then the plug changed from the original stubby T-shape, to a longer L-shape, itself subsequently re-inforced with additional strain relief. This connector shape encourages a lower-stress detatchment, but spoils the nice symmetrical property of the plug, because you can now connect it facing forwards, where it will obscure your other ports. MagSafe 2 returns this helpful feature.
So is reliability a plausible motive for this redesign? I think so. The increased contact area of the magnet in MagSafe 2 makes it quite a bit harder to disconnect by cable-tugging. The larger plug housing is easier to grip with the fingers and angle out. The connector is a sufficiently different shape to visibly distinguish it from it's predecessor. It will be interesting to see if the reliability reports from users improve.