Each week Ross Rubin contributes Switched On, a column about consumer technology.

Slates may seek to occupy a device class in between smartphones and notebooks, but they have their own dynamics. If the closest real-world counterpart for the PC was the desktop, the closest real-world counterpart for the slate may be the clipboard, a platform that aggregates and recalls important resources on the go but isn't something most people need access to all the time.

And with the change in usage comes different design priorities. Like a laptop, slates will be judged on factors such as speed, screen size, and battery life. But one spec that will take on new significance compared to other mobile devices is weight. This stems from the slate's unique hybrid of smartphone and notebook usage scenarios. The natural limits of the size of smartphones put a de facto upper limit on how heavy they can be. A few ounces isn't going to make a big difference in arm fatigue, even for most calls; there are Bluetooth headsets to alleviate longer ones. And the nature of smartphone apps also tends to favor short usage sessions.
As for laptops, there's a considerable difference between a three-pound ultraportable and a seven-pound desktop replacement on your shoulder. But within classes of laptops, the difference of a pound won't generally be a dealbreaker. And of course, once you're using a laptop on a table, weight becomes almost immaterial. This is also true of many slate tasks. If you've set a JooJoo on an exercise bike rack to watch some video or placed the iPad in Apple's keyboard dock to compose some extended text, then a pound won't make much of a difference. But for many consumers, slates will be held the way books are, in the hands. As Apple senior vice president of iPhone software Scott Forstall notes in the iPad promotional video, "It just feels right to hold the internet in your hands as you surf it." If you assume the "natural" usage scenario is using a device in your hand, a difference of a pound can make a dramatic difference.

It's hard to see anyone holding the iPad for even a fraction of 10 hours without incurring some arm fatigue.

At 1.5 pounds, the iPad is lighter than practically every laptop on the market, an unsurprising advantage given that it lacks the weight of a keyboard and hard disk. Yet, the device draws criticism for its weight, due to the unique uses of slates. While they are handheld devices, they are more likely to be used for time-intensive tasks such as watching a movie or reading a book. At the iPad launch, Steve Jobs responded to a question about the iPad's battery life being shorter than the Kindle's by noting that nobody reads for more than 10 hours. But, indeed, it's hard to see anyone holding the iPad for even a fraction of that time without incurring some arm fatigue. It does not, as Jeff Bezos has described the design goal of the Kindle, disappear in your hands.

Of course, the iPad, like many first-generation technology products, will likely get lighter over time. And with many web sites somewhat of a snug fit already on its screen, competitors coming out with nine-inch or seven-inch products may replace the burden of a heavier device with one that requires a lot more panning and zooming. Freed from such details as keyboard and trackpad design, though, engineers face a new set of challenges with slates. Suddenly, every ounce counts.

Ross Rubin is executive director of industry analysis for consumer technology at market research and analysis firm The NPD Group. Views expressed in Switched On are his own.


Switched On: The weighty issues of slates