A tip on Microsoft's Technet site explains how to regain an extra 3.5 GB of space on Windows RT. Microsoft's current Surface systems run Windows RT, which is based on the ARM processor architecture, and there are many other RT systems from OEMs.
The tip explains how to remove the WIM partition, which contains the installation files for Windows RT and other software that comes pre-installed on the Surface.
This is an advanced procedure and you can mess your system up if you don't do it carefully.
The minimum Surface comes with 32GB of storage, but about half of that is used by the operating system, applications and data. Surface does have a MicroSD slot for expanded storage.
Hat tip to Mary Jo Foley on Twitter.