Some more thoughts about the Air.

I finally saw the pertinent parts of the keynote and paid attention to the shots of the Air’s interior and of the main board. Wow, that thing is cramped; 2/3 of it is battery. There’ve been serious announcements of progress in battery technology and for the next years we can expect even slimmer machines and/or longer capacity; still, it seems that Apple now considers 5 hours (if real) as a good compromise between bulk/weight and battery life.

The Air no doubt makes use of Apple’s recent patent (sorry, no time to find a URL for it) for glueing together a precision-cast aluminum chassis – meaning very few internal mounting screws and posts, much tighter tolerances, and serious amounts of weight and dimensions shaved off, as well as better heat distribution. It also means that the case feels like a single unit; it’s significant that people who’ve handled the Air report that it feels very solid, not at all fragile like it looks. Especially the moveable port door is said to feel solidly reliable.

People calling for a removable battery no doubt are unaware that such a thing would mean a huge case opening, meaning extra ribbing elsewhere to counteract the rigidity loss, mounting screws and a good lock, what amounts to a double wall inside the unit when the battery is mounted, a pair of connectors and so forth. Meaning perhaps 200g extra in weight, 4mm in depth and $50 (at least) added to the bill of materials… all to accomodate maybe 10% of users who need an extra battery for flying tourist class?

I remember from my hardware design days how there are cascading design choices like this. Someone comes in and says “can’t we do such-and-such” and they fall off their chair when you explain the consequences. Another example is the much-bemoaned lack of peripheral ports. But consider FireWire. Yes, Apple pioneered FireWire and it’s a great technology… but check the power requirements:

…[it] can supply up to 45 watts of power per port at up to 30 volts…

That would be the entire 45W of the external power supply right there! Admittedly Apple’s other laptops already lower that to about half by supplying less voltage. For instance, the FireWire developer note says for MacBooks:

The MacBook’s six-pin FireWire connector provides unregulated 9 V to 12 V power with a maximum load of 0.75 A. Developers should design to use 7 W sustained power, or less.

Contrast this to the new MacPro, which can supply 18W per port (28W total on all four ports), and you see how laptop power design considerations are important. Supplying 0.75A to get the standard 7W on a FireWire connector would have meant larger board traces, probably a thicker board, an extra power supply chip for the higher voltage, extra dissipation, cooling… not worth it. Lowering that requirement to 5W or less would mean many external drives not working properly.

The same reasoning applies to USB. A standard USB port must supply 0.5A continuously at 5V – 2.5W. The new MacPro and the latest revisions of the laptops (including the Air) support a special high-power mode where one port can supply 1.1A (5.5W). This was meant originally to allow the keyboard to work as a powered hub, supplying the regular 0.5A on each of its ports. The Air probably needs it for its external DVD drive, although the USB Developer Note says this only works for the keyboard – and supposedly the Air’s external drive doesn’t work on other Macs. Time will tell, but here too an extra USB port would have meant beefing up the machine, though not as much as a FireWire port would have.

Somewhat more puzzling is the limitation of the 80GB 1.8″ drive, as there are larger drives sold in iPods. Either Apple is already supply-constrained for those, or the slight differences in thickness and power consumption are significant; in any event, I expect the Air’s next revision to offer larger drives. Same for RAM; coming back to the pictures of the main board, notice there’s no space for extra RAM chips, meaning that 4GB will only be possible when the next chip series doubles capacity. (And a RAM socket? With a door? Forget it.)

Finally, all this is a great opportunity for acessory makers; expect a 4-port USB hub (powered, of course) with built-in gigabit Ethernet and media slots, for instance. Even for Apple itself, it might be interesting if Time Capsule allowed a plug-in DVD drive for remote access; it would just mean a firmware update, but I suppose the Air’s drive would be too much for the Capsule’s power supply.