We have an old ReplayTV 4040 unit - well out of warranty, and - sadly - well out of decent condition. For the last little while, the device has been rebooting on a regular basis, often multiple times during a recording. So - we went out and looked for a replacement hard drive. We found a vendor who sells drives with the OS pre-installed, so we bought a larger drive than the one we had. It all looks good - it booted up, and we are now setting up the recording options. It was all pretty easy - just like the instructions here.