Re: you're obviously paying an awful lot
There are various reasons why the NonStop systems are beloved of large financial institutions, among which:
1) You never had to (or have to) take them down once a month or so to reclaim memory leaked by the OS.
2) They are the gold standard for transactional integrity so you never had to tell anybody "Sorry about your missing 10,000-share trade, we don't seem to have any record of it that I can access at the moment."
3) Programs written in the 80's are still earning their keep. Since Tandems have traditionally been back-office systems, software investments get amortized over ridiculously-long lifetimes because they don't get rewritten every four or five years as a result of language wars.
4) Tandems were designed to make their owners happy, not their programmers: the exact reverse of Unix. As a Tandem programmer since 1979, I know whereof I speak: some of the Tandem utilities and the native command shell downright clunky compared to Unix. I also recall reading an early Unix paper bragging that a development machine had stayed up for a whole week. Tandems usually stay up until a new OS rev has to be cold-loaded (months, sometimes years). ATM networks love this.
5) I still maintain venerable COBOL transaction-processing code that is not only well-amortized, but when plugged into the Tandem architecture provides NonStop, ACID database updates with absurdly scalable performance that nobody else can touch. On the multi-node Tandem architecture, systems don't failover to each other; transactions fail, get backed out and backup processes distributed across various processors pick up the slack.
Although COBOL isn't my favorite language, it's the end result that matters: mission-critical enterprise processing reality, not just the hype, and rock-solid since at least the mid-eighties. Sometimes I get to write Tandem stuff in C, but for the most part I indulge in shell scripting, Tcl/Tk, Python etc. at home. But I digress...
Getting back to the putative subject of this comment (paying an awful lot), the bottom line is that Tandem provides great TCO and a solid, scalable base for mission-critical enterprise systems. As for the alternative, you can duct-tape ten million pigeons together but it will never quite replace the 747.