Steve Jobs riding iPad

In January, we noted that the iPad was equal to 7% of the PC market.

Now, it's at 11%.

The iPad went on sale a little more than a year ago. This quarter, Apple sold 9.25 million of them. That's up 142% from last year.

According to IDC's latest estimates, worldwide personal computer sales -- not including tablets -- were 84.4 million during the quarter. That's growth of about 2% from last year.

Looking at it another way, assume that most iPads were sold to consumers, and that overall PC sales are split about halfway between consumers and businesses. In that case, the iPad has already sucked up about 20% of the consumer PC market.

Or, looking at it yet ANOTHER way, if the iPad were lined up against all other computers, it would be the fourth-biggest computer brand in the world -- after HP, Dell, and Lenovo, and ahead of Acer. Add in Apple's 3.95 million Macs, and Apple sold 13.2 million personal computing devices, making it the second largest computer vendor in the world, after only HP (with 15.3 million).

The iPad has been on sale for little more than a year. The personal computer has been around since the 1980s, and has been largely dominated by Microsoft's Windows -- with a few Macs thrown in for good share -- since the early 1990s.

Microsoft reports its quarterly earnings on Thursday. The quarter should be pretty good -- Office has been doing well for the last three quarters, and related business server software is also a strong point. But Windows sales were down 4% year over year last quarter, and nobody expects that trend to be reversed this quarter. Part of the Windows revenue decline is from strong year-ago numbers thanks to the release of Windows 7, and part of it is the decay of netbooks.

But let's be serious -- a new player just took 11% of what used to be the PC market. Microsoft's Windows monopoly, its crown jewel (and the cause of almost a decade of antitrust litigation), is no longer secure.