My current settings are as follows (for an iMac 3.6 GHz Intel Core i5) Computer Sleep: 1 hour Display Sleep: 15 mins "Put the Hard Disk to sleep when possible" IS Checked How will the computers sleep function affect Time Machine and the WD External Hard Drive? Because from articles I have read, some say that the computer will not sleep until the back up is complete. Some say, the computer and hard drive work as one (sleep at the same time, wake up together to perform a scheduled back up). Others say, never put computer in to sleep mode (display is ok) because back up will cause errors. I'm at a loss here, any suggestions would be greatly appreciated. Thank you.