Microsoft is planning to expand its Windows 8 Surface tablet line-up with a 7-inch model later this year.

At least, that's according to The Wall Street Journal. The newspaper says that "people familiar with the company's plans" have spilled the beans.

One of the sources is reported as saying that Microsoft wasn't considering plans for a 7-inch tablet as part of its initial strategy, but has changed that stance thanks to the success of similarly sized alternatives, such as the Nexus 7 and the iPad mini - which is 7.9-inch, rather than 7-inches exactly, creating almost a new category yet again.

Research firm IDC reports that a quarter of all tablets shipped in the fourth quarter of 2012 were 8-inch devices or smaller, which shows how rapidly that sector is growing. Amazon is another to have done particularly well with smaller form factor devices, with its Kindle Fire and Kindle Fire HD tablets.

It would be interesting to see if Microsoft's 7-inch tablet relies on Windows 8, as the WSJ suggests, or whether Windows Phone may stretch upwards to fill the size. Maybe Microsoft strategy is to blur the lines between both with Windows Blue, as some have suggested. We will have to wait and see.