If you're processing a very large number of transactions of some kind and require easy to validate complete consistency, mainframes are still generally king. Th

If you're processing a very large number of transactions of some kind and require easy to validate complete consistency, mainframes are still generally king. Thus their frequent use in finance and finance-like fields like transactional government services. The throughput for transaction processing can be extremely high due to things like offloaded IO, and mainframe operating systems and development tooling are very amenable to an "if in doubt, back out" approach to consistency (e.g. any failure in processing a batch results in the entire batch being reversed and left for an engineer to troubleshoot). IBM also supports a lot of extreme reliability/consistency use cases like consistency checking through mirrored processing on multiple machines. IBM also likes to argue that, for things like normal Linux VM workloads that require a very high degree of reliability, mainframes can have a lower TCO compared to approaches that rely on complex software for redundancy/failover (mainframes achieve high reliability through hardware-level redundancy, so hardware failures and repairs generally occur without any of the running software ever being interrupted). Judging by the low adoption for this kind of use I'm not sure if it doesn't pan out or it's just too hard of a sell given what's popular in the industry today. There are also more "midcomputer" options for this kind of reliability like HP Tandem and you don't see those as much these days either.