Multiple computers

I have the passport ultra on a win 8.1 laptop.  I have two win 7 computers, and all three are on a common homegroup.  Can I use the passport to backup all three computers?  How do I set that up?

If you install Smartware on all of the computers, then when the drive is physically plugged into one of the machines, then Smartware can be used to back up that machine via USB.

It isn’t possible to connect the drive to one machine and back up either of the other ones to it via the network using Smartware - for that you’d need a cloud product like a MyCloud or suchlike. You could however use a different back-up product if you have one which supports backing up to shared drives (Windows Backup can do it if you use the virtual hard drive trick - see here for some details).