I recently worked on a computer that had a single TB drive, It was bought from a store and no hardware had ever been changed.
While I was working on it I noticed it to be quite slow given the specs it had (no virus's) while rebooting I went in to the bios to make sure things were set up right.
I found that the Hard drive was set in raid, to my knowledge raid is to be set only when having more than one disk.
Later I found that the drive was failing and the computer was given a new drive, so the computer is now fine, but I would like to know if setting raid on a single drive be harmful in any way and also why would the original drive ever have been set in raid?
It shouldn't have been harmful, but could have happened if the drive were plugged into something other than the primary SATA port - the motherboard might then select RAID. (Heck, one of my ancient computers would only boot if it were in RAID mode, because that's how windows had gotten installed... on a single drive.)