Although Microsoft's 128 GB Surface Pro tablet is advertised as having 128 gigabytes of storage, the amount of space available to users is much less than that. That's also true for the 64 GB model. The Redmond, Wash., company confirmed Tuesday that the 128 GB Surface Pro has 83 GB of free storage, while the 64 GB version comes with 23 GB of open space. The reason for the difference: space already taken up by the tablet's Windows 8 Pro operating system and various preinstalled apps. The remaining space is what's available for users to store documents, music, movies, apps and other software. It's not unusual for preinstalled software to take up some the advertised space on a tablet or smartphone, but the Surface has stood out because it uses up more space than many of its peers. When the Surface RT, a lighter version of Microsoft's tablet, came out in October, its versions also had less free space than their listed capacity -- but more than their Surface Pro counterparts do. For example, the 64 GB Surface RT had 46 GB of available storage. The Surface Pro tablet goes on sale Feb. 9, priced at $899 for the 64 GB model and $999 for the 128 GB version. For users who purchase the tablet and want more space, Microsoft points out that the Surface Pro has a USB 3.0 port via which an external drive and flash drive can be attached to expand storage. The tablet also has a microSD card slot that will do the same. Additionally, the Surface Pro comes with 7 GB of cloud storage through SkyDrive, and Microsoft says that deleting the tablet's recovery partition will also free up more space.