You can easily store the blockchain (which is mostly historical data, ie. “empty accounts”) on an old (rotational) HDD because you access it in a sequential man

You can easily store the blockchain (which is mostly historical data, ie. “empty accounts”) on an old (rotational) HDD because you access it in a sequential manner, which is fine for old HDDs. It’s only the set of “non-empty accounts” (unspent transaction outputs in technical terms) that you need random access to. But this data can be stored in RAM since it’s only about 3.5GiB.