The mainframe ecosystem (both hardware and software) is sufficiently different to modern commodity hardware that ports of large applications off the mainframe a

The mainframe ecosystem (both hardware and software) is sufficiently different to modern commodity hardware that ports of large applications off the mainframe are highly risky or impossible. For organizations which adopted the mainframe way back when, the cost of staying on the mainframe is often lower than the cost to migrating to something else. It many cases, a migration is likely to mean rebuilding a decades-old codebase from scratch.