The funny thing about the Surface Pro's available memory is that, according to Microsoft, only 23GB of the 64GB Surface Pro's hard drive can be used for user files. That's odd because we only found about 20GB of system files on the fresh-out-of-the-box Surface Pro, which would leave 44GB free on the 64GB version. If true, it would really hamper the use of the 64GB Surface Pro, and practically dictates that you pick the 128GB version instead.