Digging into battery capabilities plus CPU, SSD and display power consumption can provide some hints about what the Apple iTablet might be like, at least from a hardware standpoint.

When I think about potential products, I like to think about the physics of the product: display, battery technology, and CPU technology -- in terms how much power they'll use. Sometimes that can provide insights. Natural questions arise. Is it better to use an SSD than an HDD, trading cost for power? Now that Zune HD has broken the ice with an OLED display, is it time for Apple to follow? And how much extra battery life could a low power ARM processor squeeze out compared to, say, an Atom processor? I did some digging, and the results were interesting.

The Display. There has been a lot of breathless anticipation regarding Organic Light Emitting Diodes (OLEDs). Early reports suggested that they would consume less power than conventional backlit LCDs, and that's true, but it took some time to achieve that, and one has to take into account the ambient lighting. OLEDs are hard to see in bright, outdoor light.

What's of interest here is the average power in watts/square inch. (W/in^2) By the way, that has to be one of the more bizarre technical terms I've seen, akin to gas mileage rated in kilometers per gallon. But I'll go with the flow. Here are some numbers I found:

• LCD (bright): 0.27 W/in^2
• LCD (best case): 0.10 to 0.15 W/in^2

OLED technology has come a long way. Here's a comparison of a 2004 product and the latest from a joint venture between Toshiba and Matsushita in 2008:

• OLED (28 x 27 mm product): 0.30 W/in^2 (full white, 50 cd/m^2) from 2004
• OLED (56 x 56 mm) 0.02 W/in^2 (30% of full white, 200 cd/m^2) from 2008

So while OLED looks to do well in power utilization, based on the very latest research, one has to trade that off against cost and outdoor use. For example, Gizmodo wrote that OLEDs are 50 to 80 percent more expensive than conventional LCDs.

A 10 inch iTablet screen (8.7 x 5 in) has 43.5 square inches. I found a bill of materials (BOM) for the iPhone that suggests US$3.20/in^2 for the 3.5 inch LCD (6 square inches). I'll assume that cost per square inch holds up to 10 inches. So we're looking at, very roughly, $139 (raw cost) for the 10 inch LCD and maybe $250 for OLED.

The decision, however, for LCD or OLED may have been preempted, conveniently, by Microsoft when the company elected to use an OLED in the Zune HD. Reports are that the experience in bright light is miserable, and AppleInsider suggests, with good reason that the only reason Microsoft made that choice was for marketing buzz, not user convenience or low cost.

Let's assume, then, that Apple will stay with a low cost, easy to see 10 inch LCD with a surface area of 43.5 in^2. That's a power consumption of 0.10 to 0.15 W/in^2 times 43.5 in^2 = 4.35 to 6.5 watts.

The CPU. Apple has expressed a disinterest in the Atom processor, ostensibly based on its power consumption but perhaps for those ever present, underlying technical and political reasons.

Intel quotes 2.4 watts power consumption for a 2 GHz Atom processor. However, it's widely believed that Apple, with the help of PA Semi will roll its own ARM using the Cortex architecture. That CPU is believed to use about 0.5 watt, that is, 0.25 watt for each core. That's a considerable savings over the Atom.

The GPU. Anandtech has delved into the the CPU/GPU pairing of the iPhone and discussed the ARM SGX, a system that appears to be in the one watt class. Also, there's the  NVIDIA Tegra 600 -- a device where it's realistic to also think about a power consumption of a watt or so. The AppleInsider aticle linked above goes into some interesting history of the Tegra and suggests that Apple will have its own, very modern low power design that can play HD video. And while these two examples are for an iPhone and Zune HD, I wouldn't bet against Apple and PA Semi's ability to come up with some great low power designs for a 10 inch screen.  In fact, that may be the whole cause for the delay of this product. Recall that excessive power consumption is what killed the UMPCs -- not a good thing to repeat.

Mass Storage. Digging into the issue of Hard Disk Drive (HDD) vs. Solid State Disk (SSD) is fraught with difficulties. The power utilization of both depends on the manufacturer and the kind of task assigned.

What we do know is that when reviewers test the battery life of a device, their favorite tests typically involve a continuous task, such as playing a movie or a music playlist. Tom's Hardware (see Chapter 10) did some testing along these lines and found that a selection of small SSDs (32 to 64 GB) average about 1.24 watts, with a range from 0.3 to 2.1 watts while HDDs average a little more than that, perhaps 1.3 watt performing the playback task.

My guess is that Apple is more likely to select SSDs than HDDs for a tablet based on ruggedness and reliability than the power consumption. The cost saved by using an LCD display could be allocated to an SSD instead of an HDD. Also, Apple will likely pick a SSD unit that is known to be on the low side of the power spectrum, perhaps SanDisk. Let's say 0.5 watt at load.

Battery. Looking at the battery in the 13 inch MacBook Pro, we see a 60 watt-hour unit. Because battery technology is advancing so slowly, Apple will only be able to improve on that a little in 2010. (By comparison, the batery in the iPhone is about 6-9 watt-hour.)

Most believe the iTablet likely won't have an optical drive, and the extra space in a configuration similar to the MacBook Pro 13 inch body could be used for a larger battery, but then one would have to worry about the added heft of the tablet, a device that can be expected to be held in the arm for some time as opposed to siting on a desk. Weight will be critical design driver. I'll go out on a limb and suggest that Apple, in 2010, might squeeze 65 watt-hours from a battery that's as thin as the one in the MacBook Air but a little larger in surface area.

Powering Up

Here's a tally of the power utilized, sans Wi-Fi or Bluetooth, during a battery stress test, continuous video playback.

• ARM CPU: 0.5 watt
• GPU 1.0 watt
• LCD Display: 4.4 to 6.5 watts
• SSD: 0.5 watt

I'll pick the optimistic side and say 6.4 watts total. A 65 watt-hour battery would last about 10 hours in a video playback. (By the way, that's exactly what Apple advertises for the iPhone in video playback, so holding that design spec would be a great goal.) It's also realistic to think that a much lower average power use, in casual work, might extend that considerably, perhaps 24 hours, and Apple might be able to advertise the need for recharging "every few days."

Looking at the state of the art in batteries, displays, CPUs and storage can give us a rough idea of what components might be in a proposed iTablet and how we might be using it, even of the numbers aren't exact. If any engineers out there have better numbers, please chime in. A decade ago, notebook computers could only run for a few hours, not even enough for a long cross country flight with a layover. Now, we know that Apple is working on some very low power designs and that the iTablet looks to offer the prospect of a device that we carry everywhere and routinely recharge, perhaps, twice a week.

Here's a page that has some neat concept designs for an iTablet. They'll have you drooling.

Finally, just for fun, here's a Microsoft concept video of what operations might be like on a device like this. Of course, it's a long, long road from a concept to a product that ships.