Yes, the major Italian telecommunications company stores information about every call made. There are more than one billion of them per month.

To treat this enormous quantity of data you need a mainframe and not a small one. It was an S/390 and used terabytes of storage.

When a program stops working and you can’t even kill it, if your computer is a desktop you just shut the computer down and restart it.

Don’t think that you can do the same with an S/390. To shutdown and restart it you have to wait an entire week. Not something to do very easily.

It’s a completely different way to work when you have to design and run “just” 20 queries when each query runs for many days and you have only one month to run them all.

If you make a mistake, you have to wait many days before you can correct it. You can’t afford mistakes.