I'm sure that I'm not the first person to have thought about a MacBook with a touch screen, but I think that it is an appropriate time to resurface the subject. A report by the Wall Street Journal claims that Apple will be testing devices with screen sizes of 4 inches and 13 inches.

In recent months, Apple has asked for prototype smartphone screens larger than 4 inches and has also asked for screen designs for a new tablet device measuring slightly less than 13 inches diagonally, they said. The current iPhone 5 has a four-inch screen, while the iPad has a 9.7-inch screen. The iPad Mini, a stripped-down version of its tablet computer, has a 7.9-inch screen.

Now, while a larger iPhone makes sense in a lot of ways, I don't think that a "13 inch iPad," as The Verge suggests, makes sense. There's a clear hierarchy of devices in terms of screen size. We start with the iPhone category that hovers around 3.5 inch screens. Next, we have the iPad category, with 7.9 inches for the iPad mini and 9.7 inches for the regular iPad. Next, we have the MacBook category, with screen sizes of 11.6, 13.3, and 15.4 inches.

Within this hierarchy, a 4 inch screen makes sense. However, a 13 inch screen falls into the MacBook category. A device with a 13 inch screen is unlikely to come without a keyboard, at least in the detachable form. The idea of a 13" touch screen sounds a lot like the recent Windows trend of Windows 8 Ultrabooks. Ultrabooks, essentially laptops with a touch screen, are a new category of devices. More importantly, it's a category that Apple has not yet entered.

The increasing popularity of Ultrabooks as well as the information that Apple will be experimenting with 13 inch touch screens seems to point to a "MacBook Touch" some time in the future. If that is the case, however, how would Apple handle such a device's OS? The interface of OS X is not optimized for touch, but yet a 13 inch screen with a keyboard calls for more capability than iOS can offer. Microsoft's solution is to have a touch screen interface with the "real computer" hidden under the Desktop button. Since OS X runs on Intel processors, and iOS runs on ARM processors, such a hybrid would be difficult to create since at least one of the two would need to be rewritten in a new architecture.

More likely is the expansion of the Mac App Store to include "MacBook Touch"-optimized apps. With fullscreen capability already built in, it only makes sense. Having a MacBook with a touchscreen would be really useful for iOS development. Currently, I have an iPad and a MacBook Pro 15", but, given decent specs, I think I would probably be willing to switch to a 13" MacBook Touch. I hope that Apple does indeed make its own Ultrabook.