The Apple Newton was made in Steve Jobs absence, and quickly erased from Apple's product line-up upon his return. Jobs privately called personal digital assistants like the Newton "junk."

Part of the Newton's failure can be attributed to it being ahead of its time. Part of it can be attributed to Apple's struggles at the time. And one other failure, it was a standalone device that didn't interact with Macintosh PCs all that well.

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Palm changed personal computing with the Palm Pilot in 1996. The product was success and paved the way for Palm to release early smartphones. The company was ahead of the curve, but it was eventually passed by competitors.

HP had its own PDA, the iPaq. Released in 2000, the iPaq is a "pocket PC." These things are pretty clunky and ugly, but they've done decent business for HP through the years.

In 2002 Steve Jobs said "We decided that between now and next year, the P.D.A. is going to be subsumed by the telephone." Apple didn't release the iPhone for another five years, though.

In the interim, Research In Motion released the BlackBerry which provided an invaluable service for businessmen. It was a first really popular smartphone, helping to pave the way for the iPhone and others, which in turn paved the ground for the tablet.

The iPhone is a tablet, it's just a small tablet. The iPhone software will serve as the kernel for the tablet, says Boy Genius Report.

Michael Arrington's dreamy vision of the CrunchPad was a " a dead simple Web tablet for $200." Execution of the dream proved impossible.

The price climbed from to $300, and then to $400, before finally settling in at $500, as the JooJoo. The CrunchPad caused a huge rift between Michael and Fusion Garge, the company building the tablet.

The JooJoo is still weeks from being shipped to customers, and we think it's toast.

Way back in 2000, Microsoft introduced a new idea for computing. Bill Gates called it, ''As big a transition as from DOS to Windows.'' It was ".NET" which was just an early take on cloud computing.

At the time, Microsoft showed off a bunch of new gizmos including tablets. In the years that followed, Gates talked up tablets regularly, but they never took off.

Just like his predecessor, Steve Ballmer showed off some tablets, but he changed the name to "slate." We're not optimistic the name change will mean much. When Steve showed off the HP slate this year at CES, i t was a bore.

Part of the problem is that Microsoft is simply cramming its PC software onto a slate computer. What it needs is software designed specifically to interact with this new form of computing.

A beautiful dream. Microsoft worked up a concept video, which Gizmodo landed. If it works like it's supposed to in the video, it will be awesome. But, the odds of that happening are pretty much nil. Remember the Apple Knowledge Navigator?

The Wacom is popular tablet for designers. It uses a pen to draw on and has a touch interface. We would assume Apple looked at these devices to figure out touch input and interactions.

Amazon's Kindle is called an e-reader, but it has a web browser and it's looking for developers to build applications, so we think it fits into the tablet category.

No need to explain this one. Great tablet, lots of fun. Lack of internet connectivity killing the device. We want to be able to tweet out our latest and greatest illustrations.

If you really want an Apple tablet, you can just order one from Axiotron, a California company that sells the "Modbook," a modified Mac that works with a pen and a touch screen.

Arik Hesseldahl at BusinessWeek recently profiled the company. By Arik's estimations, fewer than 5,000 Modbooks have been sold.

Lenovo debuted this sucker at the Consumer Electronics Show this year. The company calls it a hybrid notebook.

As a laptop it runs Windows. If you detach the screen it becomes a tablet running a different operating system. If the device works smoothly we think this is a pretty cool idea. It's supposed to come out in June and cost $1,000.

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Image: Jesus Diaz, Gizmodo