With the announcement of Apple’s iPad, a reoccurring theme with both of its supporters and its detractors is the fact that the iPad uses the iPhone OS, which is a task-centric (and non-windowing) operating system. For example:

I need to talk to you about computers. …

After defining the “old world” computing experience as “In the Old World, computers are general purpose, do-it-all machines” and the “new world” as “In the New World, computers are task-centric. We are reading email, browsing the web, playing a game, but not all at once.” we find:

Apple is calling the iPad a “third category” between phones and laptops. I am increasingly convinced that this is just to make it palatable to you while everything shifts to New World ideology over the next 10-20 years.

Those who are complaining about the iPad have primarily complained about the lask of multitasking:

What We Didn’t Get: Multitasking, Notifications, …
Understanding Multi-tasking on the iPad: What is it really?
iPad for Business? Not Without Multitasking

Each of these (and I picked the more polite ones) point out the iPad’s lack of multitasking–which the second article correctly notes is two things: the ability to run two applications at once, and the ability to see two applications at once.

It is entirely conceivable that we could have the second type of multitasking without the first: imagine an operating system where a process is only marked as active (and swapped in from storage) when it’s window has the focus.

In both cases, it really boils down to the WIMP (Windows, Icon, Menu, Pointer) interface: the former supporters are looking for the “next new hotness” beyond the WIMP interface, which relieves them of the task of managing multiple windows on their desktop. The latter doesn’t like the fact that a single window at a time prevents us from (for example) browsing the web while writing in a text editor–which forecloses on the possibility of writing notes in an outliner based on research material in a web browser. My common workflow as a developer is to have multiple windows open: one on a documentation site for an API, another on the code I’m writing, and several others on classes I may be using while writing my code.

But I don’t think either camp is correct.

It is clear that the small size of the iPhone makes the screen impossible to use with the second mode of multitasking, where multiple windows coexist from multiple applications at the same time. The iPhone’s design decision was to have only one application running at a time–but each application is required to save it’s complete state as it shuts down as fast as possible, which (when done right) preserves the illusion of multitasking.

A desktop computer, on the other hand, has much greater resources–including screen real estate. It would make absolutely no sense to have one task at a time running in full screen mode on my 30″ display–and there have been plenty of people who have tried to build prototype window managers for Linux which have a “one window visible at a time” model which have utterly failed. If a one-task at a time model was superior to a windowing model for desktop computers, we would have had that model long ago, given people have been experimenting with it since the 1980’s.

The iPad is clearly between the two in size and resources. It could (with its 1024×768 display) easily display a windowing interface. But the decision to do away with a WIMP interface probably has less to do with the death of windowing interfaces (as folks like John Gruber apparently believe), and more to do with product positioning: the iPad is a peripheral device, auxiliary to your main computer, which requires your computer to function. As such, it makes sense to position the iPad as a one-task-at-a-time device like the iPhone (despite the large display) and instead encourage developers to use the large display to provide a more rich one-application-at-a-time experience.

But just because the iPad is a peripheral device doesn’t mean your desktop computer is next with a one-application-at-a-time experience.

It’s clear from Apple’s design sensibilities that a main computer (your laptop, your desktop) is a main device capable of doing several things at once. And a peripheral computing device (the iPhone, iPod Touch, iPad, and iPod) is a one-task-at-a-time device which requires your main computer, but which can be carried along separately after having been docked with your main computer. (I count the iPod here because I believe it started the trend within Apple of considering peripheral devices that do only one thing at a time.)

And it makes complete sense to me that Apple would do this.

If your screen is not big enough to display multiple windows at a time, then why put the infrastructure in place to support multiple windows? (I’m looking at you, Windows Mobile.) If your device is not big enough to display windows, then why put the infrastructure to have multiple windows?

And with the exception of two category of applications (those which play music in the background, like Pandora, or those which periodically poll services like an mail application or IM application), why even support multiple applications at once? Do we really need (as we have in Android) the ability of your game staying resident in memory when you’ve swapped tasks to read your e-mail? (After all, the fact that an application stays resident in memory on Android means your process memory space is limited to 16 megabytes of RAM–as opposed to the 100+ megabytes you get on the iPhone.)

A peripheral computing device which does not support multitasking can also be made with less RAM, less CPU power–since it only needs to do one thing at a time. Because it is peripheral and only supports one thing at a time, applications can be built which take full control of the display without worrying about other applications. And the UI can be streamlined and use a completely different model than the WIMP environment.

If you were expecting the power of a tablet computer (a’la a Lenovo ThinkPad running Windows 7) because you see a tablet computer as a main desktop computer that uses a pen or your finger, and not as a peripheral device–then buy a tablet computer. Lenovo makes very nice laptop computers.

But I’m glad Apple decided to make the iPad a peripheral device: I think it was the right decision to release a new type of device rather than releasing a small notebook computer without a keyboard.

Because that’s what a tablet computer (a’la Lenovo) is: a laptop computer either without a keyboard or with a keyboard that can be tucked away.