I have a Seagate Barracuda ATA11 7200 40GB drive as master. I also have a Western Digital 5400 20GB drive that I would like to use as a slave. My question is: will the lower rated Western Digital drive slow my system down, even if I only use it for backing up little used files?
If you have two devices running off the same IDE port via one ribbon cable then both drives will run at the lower speed, although you probably won't notice any reduction in speed. I do this and don't have any problems with it at all. I have a simple batch file that copies newer versions of files from my master drive to my backup.
If you use your second drive just as a back up, have a look at XXCOPY at click here for a free, quick and easy program which copies everything from one disc to another (including System, registry, programs and datafiles). Used it for over nearly years now.