How large a hard drive for the Novatech U50SI1 take?

Can someone tell me how large a drive can a Novatech U50SI1 take?

This machine would use a 2.5" SATA drive.

If you are referring to capacity rather than form factor, that is an OS limitation not hardware limitation.
You need the drive to be formatted as GPT for greater than 2TB drive support, which isn’t possible under older Windows OS.

I hope this helps.