A bank based in my region, one of the biggest in Europe, uses IBM mainframes and has hundreds of thousands of COBOL programmes. Their availability is disastrous. They need to regularly reboot LPARs (logical partitions of the mainframe) because they're so brittle, resulting in a segment of the clients unable to use online services. And on the other hand, services that need to stay available, like websites or instant settlement, obviously don't run on mainframes. That means that the website is up... but only displays a maintenance message.