I'm looking at battery backup units and I'm trying to figure out how much power the iMac draws so that I can better evaluate what unit to buy. I'm looking at a CyberPower unit labeled 550VA/330W. I'm not sure how to read that but I'm thinking it means it would run a 330W draw for almost two hours (550/330=1.67). I'm probably totally off there but still, finding out how much the iMac draws seems like the first step in understanding what I'll get out of an uninterruptible power supply. I would expect the best number to have is what it draws in sleep mode. If I'm using it and power goes off, I'm sure there'd be enough power to shut down normally with just about any power supply. But, if I'm away from the computer and the power goes out, it would most likely be in sleep mode (it certainly will be after 20 minutes) so that seems like the useful number. Any help understanding this would be appreciated.