There is some peculiarity stemming from the fact that there is (ahem) to be no driver on the disk. The driver is loaded from the machine on booting, for some reason.

Apple specified an unformatted hard drive in cases where hard drive replacement was required. But where would you get a suitable (small) one of those these days?

I've tried installing a new drive before with some of my small IDE laptop drives and gotten nowhere, but there must be a way. I shall tinker.... The trouble is simply that the original drive is a bit noisy.