The rumor of Apple debuting a smaller iPad - dubbed the iPad Mini - has been consistently reported, but never confirmed by Apple. Multiple sources including The Wall Street Journal and Bloomberg have heard that an iPad Mini is coming, as early as September, so what could be the key differences?

The plan, Bloomberg said, is for Apple to go against Google and Amazon - the former debuted the 7-inch Nexus 7 tablet on June 27, at its Google I/O conference - to "help maintain dominance of the tablet market."

The chief difference between the two tablets will be the screen size: the iPad Mini will offer a 7- or 8-inch display versus the regular iPad's 9.7-inch, according to sources familiar with the matter. The consequence is that the Retina display - Apple 2048 x 1536 display - won't feature, probably a move to drive down cost and get closer to the $199 price point Google and Amazon - with the Kindle Fire - is offering.

"It would be the competitor's worst nightmare," Shaw Wu - Sterne Agee & Leech analyst - said to Bloomberg. The 7-inch form factor was seen as an untouched market by Apple, and in some ways an advantage over the current iPad in terms of weight compared to the 9.7-inch display.

Research firm Gartner claimed Apple controls 61 percent of the tablet market, which is estimated to be worth $66.4 billion during 2012.

Of course Microsoft announced two Surface tablets, running Windows 8. There's Windows RT for Surface - a a cheaper, less powerful, feature-limited version of Windows 8 designed for devices on ARM chips - and Windows Pro for Surface, a more expensive and feature-rich version of Windows 8. While the Nexus 7 debuts around mid-July, there's no release date for Surface. It's expected to debut alongside Windows 8.

If Windows 8 releases in October as expected, with Surface, then the iPad Mini could be stiff competition. Apple is pushing the iPad 2 as a cheaper device for $399 versus $499 for the new iPad from the Apple Store; the former is even cheaper on eBay.

There's still the question of connectivity: Microsoft's tablets don't have a price, but do offer USB slots. It's a small but effective inclusion, helping the device to be seen as a productivity device which is essential for the Windows audience.

The iPad Mini's display will be the same as the iPad 2's pre-Retina display. If introduced, Apple will potentially have four screen sizes for developers to scale apps across: the 3.5-inch display on current iPhones, a potential 4-inch iPhone, the 7- or 8-inch iPad Mini and the 10.6-inch iPad.

It could also mean Apple has three product announcements a year: the bigger iPad around March, the iPhone in the fall and the iPad Mini shortly after in October.