Microsoft's original Surface Pro storage estimates, that the company supplied to The Verge, are incorrect. In a series of tests, Ed Bott over at ZDNet has found that a 128GB model of the Surface Pro actually has 89.7GB of free usable space compared to the incorrect 83GB figure. It appears the reason for Microsoft's mistaken values stems from a difference between pre-production and final shipping hardware.

Final Surface Pro models shipping with more storage than expected

"A source inside Microsoft tells me the employee who confirmed the numbers did so using pre-production machines that contained different disk images and debug code that is different from final shipping units that will be on sale beginning this weekend," explains Bott. The result is that the Surface Pro 128GB model gets around 8 percent more space than Microsoft originally estimated. Microsoft's own figures suggested that a 64GB model would only have 23GB of usable storage, but the company revealed earlier this week that final production units are shipping with around 6-7GB of additional space.

Removing a recovery partition from the Surface Pro will also free up additional space. Bott found that the partition accounts for 7.81GB of space on the 128GB model. Bott claims that when it's deleted there's more free space on a 128GB Surface Pro model than a comparable 128GB MacBook Air. If the partition is left in place then there's 89.7GB of space vs. 92.2GB on a MacBook Air.

We have reached out to Microsoft to confirm the exact storage figures for the 64GB model, but it appears it will be around 30GB of free storage, approximately 30 percent more than Microsoft originally quoted.

Update: Bott has updated his report to address some inaccurate MacBook Air storage data. The 128GB MacBook Air still has more free space than a 128GB Surface Pro even if the recovery partition is removed.