Hewlett-Packard is the largest PC maker in the world, significantly outpacing even longtime rival Dell these days. So it was more than a bit of a shocker today when the company announced plans to spin off or sell its personal computer business.

By the same token, HP spent more than $1 billion to acquire Palm and its webOS a little more than a year ago. Which made it even more of a shocker when the company said today that it would be discontinuing its webOS device sales — including the TouchPad — and re-evaluating the future of the mobile operating system.

But digging into the underlying trends, even our rudimentary chart gives a sense for where things are headed. We can only imagine what HP CEO Leo Apotheker is seeing in the numbers available to him.

Reflecting trends in the broader PC market, HP’s computer shipments have essentially been flat over the past couple of years — in large part because people are spending their money on iPads rather than lower-cost PCs when it comes time to buy a second or third machine in the home.

HP’s decisions today were “shaped heavily by secular market trends that are redefining how technology is consumed and deployed,” Apotheker said in announcing the news.

In short, Apple’s fingerprints are all over both of HP’s decisions today.

So where does this leave companies still relying on the traditional PC business? Time will tell, but this much is clear: Microsoft CEO Steve Ballmer had better hope those Windows 8 tablets are the best thing since the ham sandwich. September can’t get here soon enough.

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