text: How long is a piece of string?  A hard drive can function indefinitely sans manufacturing defects or extreme heat.  I have 2 primary hard drives and 2 external drives running on my machine 24/7, only rebooting when a necessary update is required and things are fine.\n\nA hard drive is the only mechanical part of a computer and as such will at some point fail.  BUT when that is can not be predicted.  I would say 90% of the time it would work faultlessly until you are ready to change your machine