They&#x27;re more likely to use mainframe database systems with the verification done in apps that interface with it or do batch runs on it. The mainframes and databases themselves cover the integrity and availability portions. So, it&#x27;s a ledger in practice but not directly stored as one.<p>Matter of fact, storing it as one is incredibly wasteful. Banking systems have shown it&#x27;s not necessary. Just need the transactions, timing, sources, and verification of them.