Surface Pro and MacBook Air have similar free disk space
In a lengthy report, Bott crunched the numbers to discover the Surface Pro and MacBook Air contain very similar amounts of free space after the OS and other partitions are factored in. The MacBook Air in its stock configuration has 92.2 GB of 128 GB available for use (77.3%), while the Surface Pro comes with 89.7 GB free (75.2%). A significant portion of the Surface Pro's storage is taken up by a recovery partition, which if you choose to remove (at no cost to system capabilities) nets you more storage, increasing the amount of free space to 97.5 GB (81.8%).
It's also worth noting that Mac OS X and Windows report storage capacities in different ways. OS X likes to use the decimal (Base 10) system, meaning a drive advertised as 1000 GB will show up as very close to 1000 GB in the OS; Windows, on the other hand, uses the binary (Base 2) system, meaning the same "1000 GB" drive will show up as only 931.5 GB.