Hi cy555,
Thank you for reaching out Microsoft Community.
It can carry up to 1 TB of SD card and for compatibility, you can check this link https://support.microsoft.com/en-us/help/4495650/surface-what-sd-cards-are-compatible for details. You can also review this relevant link https://support.microsoft.com/en-us/help/4036290/surface-storage-options#removablestorage for reference.
If this answers your question, feel free to mark this post as an answer. Otherwise, don't hesitate to respond to this thread if there's anything else that needs to be addressed.
Kind Regards,
Crest_Z