The blockchain is often noticed as a remarkable database, that is reliable and is handled by an independent network. That reliability seems something to exploit for other purposes. But the reality is that the database is small and expensive. It is authenticated, and allows validated transfers of bitcoin.

Every 10 minutes, an expensive network of machines processes the blockchain, and produces a new validated record. And is paid at 25 bitcoins. Unless there is payment, the process stops, and no database is handled. The cost is a reasonable part of the bitcoin transaction system. But it is a bit expensive for ordinary data.