Opening a local disk folder with Hyperlink

Having problems trying to open a local disk folder in a Hyperlink field

Opening a shared folder works e.g. \\share\folder\data

but

refering to a disk does not e.g. C:\Folder\Data
I have tested a number of variations of a local disk reference but none work (e.g. file://C:\ or //c:\ )

Field is of type text and folder reference is entered as above
Am I doing something wrong?

Thanks in advance

C