The reason for this is actually pretty interesting though. Historically it was just a US/UK English difference, but it evolved into both being used because one of the first big manufacturers of optical discs, Philips, called them discs, while the US-based IBM spelled their magnetic disks with a K.
I just remember it intuitively based on vibes. Stalagmites sound bulky and lumpy, and stalactites sound sharp and light.