You can’t believe how many times I’ve been asked if you can listen to music while browsing the web on the iPad. Or rather, I’ve been “told” that this was the case, with varying levels of certainty.

As anyone who has ever used an iPhone for more than 15 minutes knows very well, this is simply not true. You can listen to your music while browsing the web. In fact, you can do much more.

Multitasking is the ability of an operating system to run multiple processes (tasks) at the same time¹. The last non-multitasking operating system I used was MS-DOS. Of course other single-tasking OSes have been released after DOS², but the iPhone OS is, and has always been, a multitasking OS.

What this means is that the iPhone, and therefore the iPad, is capable of running multiple applications simultaneously. In fact, 20 applications are running simultaneously on my non-jailbroken iPhone 3GS right now³.

So, to answer the question explicitly: yes, you can listen to music while you’re browsing the web on the iPad. iPod is always running in the background, even if you’re not listening to music. Mail also always runs in the background, so you’ll be notified when you have new mail. Finally, thanks to push notifications, you’ll be able to receive Facebook notifications, MSN messages, etc. while you’re reading an academic paper, writing an email, or browsing the web.

Restrictions

So, what is this “lack of multitasking” people can’t stop talking about? Apple does not allow third-party applications downloaded from the App Store to run in the background. The reason for this is simple: battery life. When an application is running in the background, it uses the CPU, and therefore drains your battery.

Battery life is very important for a mobile device; everyone wants more battery life. But everyone also wants lighter devices. Otherwise, Apple could always build an iPad that has 100 hours of battery life but weighs 5 kilos.

Let’s consider how we use multiple applications simultaneously on our computers: we either have some applications (email/IM client, music player, etc.) running in the background, or we have a two or more applications running side-by-side on the same screen (a web browser and a word processor, for example).

Push Notifications

As I’ve said before, your email client and music player are already running in the background on the iPhone OS. Technically, you can’t run IM clients in the background, but thanks to push notifications, you’ll continue receiving your messages. Apple actively encourages developers of such applications to take full advantage of push notifications, and almost all such applications (Facebook, all important IM clients, some games, etc.) already support them.

I agree that push notifications aren’t perfect, and that they don’t work for all applications. For example, a Twitter client could check for new tweets periodically if it could run in the background (and this is what most desktop Twitter clients do), but it’s infeasible to use push notifications for Twitter⁴.

Be that as it may, I argue that responsiveness and battery life are still more important for most users. The iPhone’s CPU simply isn’t powerful enough to run more than a couple of third-party apps in the background and still maintain the responsiveness of the frontmost app. If, however, the new A4 chip is powerful enough, Apple could let at least some third-party apps run in the background and leave the decision about battery life to the user.

Now, let’s focus on the case where you run two or more applications side-by-side on the same screen.

While realizing that this might be an issue for some people, we also have to realize that iPhone OS devices (iPhone and iPad) do not have enough screen real-estate to fit two or more applications and the keyboard on the screen, and still remain usable⁵. The iPad’s screen has a resolution of 1024 by 768 pixels, while the iPhone has less than 20% the number of pixels with a 480 by 320 pixel screen. These resolutions almost halve when the keyboard is displayed.

In lower resolutions like these, you switch between applications instead of running them side-by-side. This is what everyone was used to doing before high-resolution displays became commonplace a few years ago. Most netbook users I know still complain about, among many other things, being unable to fit two windows on the screen.

Full Persistence

There’s still one fundamental difference between iPhone OS devices and general purpose computers, though: you can’t minimize or hide an application on the iPhone OS. But here comes the best thing since sliced bread: full persistence. Apple uses full persistence in all their iPhone applications, and encourages all iPhone/iPad developers to do the same.

But what does full persistence mean? It means when you quit and relaunch an application, the application will be in whatever state you left it in. If you quit Facebook while you’re looking at a friend’s profile picture, Facebook will be showing your friend’s profile picture the next time you launch it. If you were in the middle of a sentence when you quit Notes (or Pages), you will be at the same place, having lost not a single word, when you relaunch it. This is known as full persistence, and it blurs the line between minimizing or hiding an application and quitting it.

Of course, I have to admit that the current state of full persistence on the iPhone OS isn’t without its problems. The most important issue is that not all applications support it. The main reason behind this is that it’s a lot of work to implement full persistence for a reasonably complex application. However, I expect Apple to add OS-level full persistence support in the near future.

Another problem is that there’s no Command-Tab equivalent; you have to go through the home screen to switch between applications. I also expect Apple to provide an easier method for switching between applications, at least on the iPad.

Conclusion

Apple has very valid reasons for restricting multitasking on the iPhone, and I don’t see them making any changes with regard to multitasking on the iPhone anytime soon, at least with the current iPhone devices. Some of these reasons are less valid on the iPad, and I believe Apple will at least make this restriction much less noticeable in a future software update, possibly 4.0.

Finally, TidBITS has recently published an article on the same issue entitled “Does the iPhone OS Need Multitasking?,” which is well worth a read.

P.S. First post in 10 months. I’m back, baby!