That's right, folks. Hewlett-Packard (NYSE:HPQ) will be releasing a massive 21.5-inch tablet, which hardly qualifies as a mobile computing device. Despite the impracticality of traveling with a 21.5-inch tablet that has no battery, HP's newest brainchild will run Google (NASDAQ:GOOGL) Android, sport an NVIDIA Tegra 4 processor, be compatible with a mouse and keyboard, and include a kickstand to prop it up like an all-in-one device. Perhaps the most surprising element of this announcement is the price. Starting at $400 and available in September, this tablet-meets-all-in-one device retails for half the current MSRP of HP's cheapest touch-enabled Microsoft Windows all-in-one PC.

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A HP Slate 21 AIO mockup. Source: HP.

It's for the family
As easy as it is to dismiss the Slate 21 as a massively impractical tablet, HP may not be that crazy after all. The company has positioned the device as an affordable all-in-one PC alternative for families that want a rich yet simplistic user experience. The added affordability can be attributed to the open-source nature of Android and a much cheaper Tegra 4 processor, giving the Slate 21 a healthy pricing edge over Windows-based all-in-one devices. For families that live mostly in the cloud, the Slate 21 may turn out to be a palatable choice.

Why Android?
What's baffling to me is why HP went with Android for an all-in-one device. because Android is in no way optimized for desktop use. If HP was aiming to save on operating system licensing costs, you would think that Chrome OS would be a more natural fit, since Chrome OS is specifically tailored for desktop use. Not to mention, the whole goal of Chrome OS is to offer a simplistic and secure user experience for those that spend most of their time on the Web. Isn't that exactly what HP is after with the Slate 21?

I think HP's reasoning is grounded in Android's massive worldwide user base. Last month, Google announced that 900 million Android devices have been activated to date. Perhaps HP is hoping a widely used operating system like Android may make the Slate 21's user experience more familiar, and thus more desirable. We'll have to wait until September to see how this all-in-one experiment pans out for HP.

Fool contributor Steve Heller owns shares of Google. The Motley Fool recommends Google and NVIDIA and owns shares of Google and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.