OK, suddenly you get the S.M.A.R.T. message that your harddisk is out of order and beyond repair: you should have it replaced. Well, Time Machine has been working for you, so what could go wrong?

It seemed to be a good idea to substitute a 500Gb SSD for the 1Tb HD. I checked out some YouTube videos to see how the iMac could be opened (the only screws detectable are for the RAM compartment, and they’re good for nothing). I bought a Samsung 2.5" SSD of the newest generation and an adapter in order to fit it into the iMac’s 3.5" slot. After disassembling the computer I discovered three plugs: for data, for power, and for temperature. That was a surprise, as the adapter only had two connections and lacked the one for temperature. I tried it anyway (and naively glued the temperature plug to the adapter’s surface). That didn’t work. After some desperate attempts to get the computer started I bought a 2Tb Seagate Barracuda, which offered the (apparently) necessary connectivity.

Sadly, copying the original HD to the new one didn’t yield the desired result: the iMac remained dead. The data must have been corrupted in some way; after all, the original HD was broken (even if still functioning...). Eventually, I copied the contents of our MacBook to the new HD, and that did the trick. My iMac now thinks he’s a MacBook, and it was –and is– a lot of pain to update the system from 10.6.8 to 10.10.3 and to restore my “valuable data” from the Time Machine disk. Most things, however, seem to be in order now... When I’ve fully recovered, I might put the SSD in the MacBook and replace the iMac’s long defective SuperDrive. I know now how it is done.