ignoring hardware its all down to the filesystem. for example FAT32 has a limit of about 80GB before it gets useless. Also FAT32 has a maximum file size of 4GB. NTFS on the other hand has no limitations that currently exist, though the max filesise is in the 16 Terabyte range, so this is currently not a problem. This is per disk not as a total.
Then you just got to look at your hardware to see what the current max supported size is.