Mobile phones as PC replacements? I don't think so...

One of the greatest myths in the mobile industry (and IT industry) is that we are in the "post PC" era. The noise and hype around smartphones and lower tier devices replacing normal computers remains deafening.

(There's also a growing clamour that iPads and other tablets are shaking the PC market to its core, but that's a slightly different issue I'll deal with another day).

I've written about this before, but there's still a ton of ill-informed noise, usually from people who have long held a grudge against Microsoft, and see the rise of the smartphone as a way to realise their wishful thinking. Unfortunately, they let their glee cloud their critical judgement, asserting that a handset can easily replace a notebook, once it's got a TV-out port and a basic OS.

I've covered this issue before, but one new statistic has just helped me crystallise my thinking:

A typical smartphone battery holds 10-20x less energy than a typical laptop battery

In a simple nutshell, that represents the difference between the two worlds. In a computer, that extra power is used to make the screen brighter/larger, and also to run the processor and ancilliaries harder. For all a phone's great power-management tricks on standby (and indeed much-needed cleverness when it's being used as well), the bottom line is that their "ain't no substitute for energy".

Laptop shells are bigger, supporting a larger battery. Not only that, because they are dependent on volume, a 2x increase in each dimension results in an 8x volume and therefore energy storage capacity.

The result: the two devices remain in different universes. Yes, in the big Venn diagram of "use cases", there are a few areas of overlap. I certainly use smartphones *a lot* for certain tasks - but there's no way I'd be writing this blog post on one, with the need for a decent keyboard, and a screen large enough to have open windows from various web pages & background apps.

For those wanting some harder numbers, the key metric is "Watt-Hours", not the more common "mAH" (milliamp-hours) you see on handset websites, because power (watts) = amps x volts, and different devices operate at diferent voltages. Watts = 1 joules [energy] / sec, so a Watt-Hour is a proper measurement of *energy* (3600J to be exact).

Some data points:
Nokia E52 = 5.5 W-H
iPhone 4 = 5.25 W-H
BlackBerry Torch = 4.7 W

MacBook Pro = 77.5 W-H
Dell Latitude = 85 W-H
HP Mini netbook = 66 W-H

EDIT - an Apple iPad has 25 W-H of battery life, hence its position further up the curve. 5x that of a smartphone, but 3x less than a laptop. More of a threat, greater overlap on some use cases, but still in a different world.