Large banks typically have very scalable front-office trading systems which can process hundreds or thousands of trades per second. Most of these are distributed systems running on large numbers of commodity PCs, usually running Linux.
However the back office booking systems are typically mainframe based. These systems cost literal millions per year for just the hardware and licensing alone.
I often hear anecdotally that there are specific advantages to the mainframe architecture for this particular job. Can anyone explain what the differences are and why they are worth the money?
Or are mainframes now used simply because of their inertia in terms of existing proven software and availability of people with the right mix of business and software skills?