Hello all what I want to know is there an upper limit on the size of microSD card than can be put into this board.
Thanks
Richard
Good question …
What I could find: Max partition on a disk is 2Tb in ROS6 (Source: wiki) and 14.7Tb in ROS7 (source: help) so you should stay below or partition the device to comply.
https://wiki.mikrotik.com/wiki/Manual:System/Disks
https://help.mikrotik.com/docs/display/ROS/Disks
What are you planning to do ? 
Nothing planned But There is no mention of memory card max size in specs for the routers just says microSD. But 2Tb makes you think what you could do.
Don’t plan on putting any NAS function on it. It would be way too slow.
No I agree there. But I am sure there are things it could be used for.