Wd My Passport Ultra Software

Samba is a linux protocol/program that creates a network drive on a 'server', this server could be your router for example, there are plenty of modern routers that support a USB-drive to act as a Samba drive. The advantage of Samba is that, once connected to it, the PC/Mac will recognise it as a standard drive, regardless of the filesystem of that drive (which is usually a Linux FS, for example NFS). The disadvantage is that it is indeed a network drive, so without the right infrastructure it is considerably slower than a local drive and of course susceptible to 'random network problem events', this is why I mentioned it requires at least some knowledge of networking. Considering you want local access, you could format part of your WD to be Mac friendly and the other part to be Windows friendly, I believe someone else in the thread already mentioned that option?