Never mind those three. Quake at the providers you don't think of first: IBM, HP and Fujitsu.
I've worked at 3 banks in the last year, and two of them are big players that you will know. Every one of them has outsourced their IT to IBM and the 'IBM Cloud'. Outsourced as in
(a) IBM now own all the IT kit. Bank leases it back.
(b) All our infrastructure is run by IBM
(c) Some of our IT knowledge was transferred to IBM during ramp up. We fired the rest.
Modern banks are basically data centres with a banking license ( they are busy closing those expensive 'real' branches as fast as they can.) If IBM flops in the next downturn, the 2007 crash is going to look like nothing, as all the banks that rely on them fail.