

CPUs don’t make something a mainframe, the whole system design does. They’re transaction-based throughput monsters with all kinds of bells and whistles when it comes to reliability, seamless fallover, etc. The European CPU initiative currently focuses on supercomputing (weather simulations and such) which is a completely different beast when it comes to dataflow but certainly a good foundation for general compute.
Looking into my crystal ball, at some point SAP is going to enter the hardware business.
When you’re looking at your bank balance you’re seeing bank Euros, for which your bank has to hold a certain percentage of actual (central bank) Euros in reserve (that’s what fractional reserve banking is about: Not just the central bank, also ordinary banks can create money), when you transfer money to another bank the receiving bank will have to make sure that it has enough central bank Euros to back up the recipient’s balance. SEPA is a standard interface and procedure to negotiate such transfers.
The Digital Euro is central bank money, just as bank notes and coins. It’s a (possible) step towards a full-reserve banking system without having to actually keep actual notes and coins around. And the ECB is very aware of this which is why they’re talking so much about limiting how many digital Euros you can hold at one time so the current banking system doesn’t get completely up-ended over night.
…if that doesn’t really answer anything then that’s because money is fucking complex, and how our system works is completely unintuitive. But, essentially, Digital Euros are the same stuff as money under the mattress, just digitally.