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The "Bring Your Own Device" philosophy spreading through enterprise is proving a real boon to Apple.

The company is expected to sell $10 billion worth of iPads and $9 billion of Macs to business customers in 2012, according to Forrester's latest Global Tech Market Outlook. Those are 68 percent and 45 percent increases, respectively, over 2011.

And in 2013, spending on iPads and Macs could hit $16 billion and $12 billion respectively. Slowly but surely Apple is making inroads into enterprise, a sector traditionally dominated by Microsoft. And as Forrester notes, that is somewhat unexpected.

"The biggest disruptive force in the computer equipment market thus is ... Apple," the research outfit said in its report. "This is a surprise, because Apple has not and does not directly address the corporate market, while turning a wide variety of consumer technology markets upside-down. But its rapid growth in the corporate market has been the big surprise of 2011, and it will be even more of a factor in 2012."

How can that be when we so rarely hear stories about big enterprise deployments of Apple hardware? As Forrester explains, "The Apple assault on the corporate market has so far taken place without much formal Apple support, and probably without Apple itself understanding its full extent. That's because corporate adoption of Apple products has been largely clandestine."

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In other words, employees are buying iPhones and iPads and sometimes even MacBooks as well, while enterprise is increasingly supporting them on the back end. Sometimes, it is even subsidizing them, or their use.