When you looking to buy a device like the Surface you have to decide which storage option to go for, there is the 32GB version or the 64GB option but working out what actual free space you would have to play with is hard to work out. Microsoft have published a guide to what space is available to the user on a new Surface and it’s interesting to see what is using up the space.
Before you start 5GB is reserved for Windows recovery tools and 8GB is used by Windows RT, Office and the built in apps. So on a 32GB device you would get 16GB free and 46GB free on a 64GB Surface for you to play with. If you need to add extra space you can use the MicroSD card and with a little workaround you can use the SD card for your music and videos.
On my 32GB device I have around 12GB free after installing the apps I need which is not to bad and I have 32GB SD card for media.
You can read the details on Microsoft’s post