Apple iPad, Galaxy Tab, Dell Streak, and iPod Touch. Should any of these be considered a PC

Is an iPad a PC Depends on who you ask.

It's true the way we use personal technology now is changing, making what we refer to as a "PC" a moving target. Recently, some market share studies have grouped tablets with traditional PCs to show how power in the laptop and desktop market is shifting in favor of, well, Apple, a longtime underdog in the PC world.

That's sales numbers we're talking about, of course: at more than 10 percent, Apple's Mac sales put it at its highest market share in the U.S. in ages but still nowhere near HP's worldwide market share of more than 17 percent. Cupertino's influence, however, is much more broad' you need only glance at the design and marketing of most computers sold today for proof.

But is it fair to group PCs and touch-screen tablets together if only to illustrate Apple's ascendancy in the industry

Not yet. The touch-screen tablet and a PC are still different devices in terms of what they enable us to do. Certainly, there are overlaps: both allow you to watch movies on a decent-size screen, you can connect a tablet to a full-size keyboard and get a lot of typing done--e-mail, documents, you can even create presentations, read e-books, and of course, browse Web sites on a display without having to squint.

But it will be a rare iPad or Android tablet user who will tell you they've been able to completely replicate what they were doing on a MacBook or an Acer laptop, or Dell desktop on a 7-inch or 9-inch screen--a display at least 12 or 13 inches is what most PC users would regard as "normal." These media tablets don't have full desktop operating systems, storage is limited, a virtual keyboard does not replace a physical one, there are limited ports, there's no file system, and the most-used productivity apps we use for work don't necessarily translate easily to these devices.

While you can do many PC-type tasks, it's easy to argue that for most users the touch-screen tablet experience is just not the same because of some basic limitations. At times, it's "a question of degree," noted Bob O'Donnell, PC analyst for IDC, a firm that does not include tablets in the same bucket as traditional PCs. "I just got back from two weeks in Asia, so I'm two weeks behind on e-mail," O'Donnell offered as an example. "I can do some, but there's no way I'm doing 300 e-mails on an iPad."

The difference in how people are actually using media tablets is all about context--the task you're doing and where you are, he argues.

But that's not to say tablets won't replace PCs for many people some day, even soon. Smaller, more powerful devices still to come are inevitable, and those will enable us to do more traditional PC functions on different and smaller form factors. And of course, over time habits and usage scenarios change.

Michael Gartenberg, analyst at Gartner, argues that a tablet may already replace a PC for some people, even if it's not their primary PC, which we can define as the computer that they use to store most of their data and sync their phone or music player.

Someone might buy a Galaxy Tab instead of a Netbook, which is typically recognized by the industry as a mini notebook, or a college student might be limited by funds and choose an iPad instead of a laptop, he pointed out.

Not everyone uses PCs the same way, so a tablet might function as a PC for some people, even if experts and analysts insist the two are separate, Gartenberg added.

"Someone's primary PC is someone else's casual PC," Gartenberg said.

How the average soccer mom, Silicon Valley engineer, or high school student are using devices and how those devices are being marketed to them gets at the heart of the very murky and continually shifting definition of how we define a computer.

The Logitech Revue with Google TV isn&39't all that different on the inside from an Atom-based Nettop computer.

The extremely mobile, app-friendly mode of computing many of us recognize from using an iPhone or an Android phone is being replicated in form factors that we're used to seeing on more traditional PCs, including Google's Chrome OS coming soon to Acer and Samsung mini notebooks. With those small laptops, there will be no traditional OS, it's a small notebook that only runs a browser and has its own app marketplace, the Chrome Web Store. Apple's next major update to its desktop operating system is also going to be geared more toward downloadable third-party apps, with the Mac App Store.

The confusion over how to categorize gadgets isn't likely to be limited to analysts and marketers though. When you're considering buying one of these devices, it's not at all clear sometimes if you need a smartphone and a tablet, or a smartphone and a laptop, or all three.

The lack of clarity over what is a tablet or what is a PC and in what situations you use them extends beyond those devices too since so many gadgets are taking on computer-like characteristics. Take the Nook Color from Barnes & Noble. It's marketed as a competitor to the Amazon Kindle, which is to say, as an e-book reader. But the Nook also runs Android, looks an awful lot like a tablet, and can browse the Web.

And what about Google TV One of the first devices on the platform, the Logitech Revue, is a set-top box that has an Atom chip inside--traditionally used in mini notebooks, runs a smartphone-oriented OS in Android, Gartenberg points out. In other words, it's not going to get easier to define these categories of what is and isn't a PC anytime soon.

"The problem is, we want clarity," he said. "It's important to understand what these (market share) numbers look like, but as we face more convergence and have devices that do more things, counting them is going to be trickier."