The XF551 can read PC disks (as in: formatted on a PC for use with Windows). Will the XF314 be able to do so too? Or maybe even write files to them?
The SF314 drive mechanism is fully compatible with PC 3.5 DD disks. As a matter of fact, you can say it is the equivalent as the XF551 drive mechanism but for 3.5 disks. In both cases you need custom firmware and software, of course. But actually the 314 would be more compatible with PCs. This is because you don't need to overclock the FDC as the XF551 needs for backwards compatibility. This means that you would use the same bitrate as a PC.