Any size you care to throw at it. If you have Windows XP and have not installed SP1 then there is a windows limitation in that it will not be able to see any more than 137Gb.
The motherboard will not limit the disk siae you can have.
Surface Pro (2017) vs Surface Pro 4
20 groundbreaking 3D animation technologies coming to Siggraph 2017
iPad Pro 12.9 vs Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.