The M4 Mac mini came with a surprise — a slotted and upgradeable SSD. Here's how to install one, get it running, what to expect for speed, and what's happened in the last eight months since upgrading.

Have you ever looked at your cat as it stared at a blank wall and thought, “What is he or she thinking?” I certainly have, and I’ve done the same thing with my SSD too—wondering if it was doing OK, if ...