Deca means ten in Greek. Octo means eight also in Greek, but when octo is used in composite words it becomes octa-.

Therefore, deca-core, means ten-core and octa-core means eight-core. Why are we using Greek words to describe the CPU or other hardware or software features, when we could very well use modern English? After all, we say “cores” instead of “pyrines” (the Greek word for “cores”).

We use Greek in thousands of English occasions in science, medicine, astronomy, philosophy, anywhere… The very word “philo” (=I am a friend of) is Greek, and it is used in a lot of cases. Or think about “astronomy”, a word made from two Greek words “aster” and “nomos”. “Mathematics” is Greek, “Philology” is Greek, “Technology” is Greek!

My guess is that technology companies use Greek because (and when) they sound nice being also strange, unknown, becoming simultaneously sources of interest and prestige.