People tend to think migrating an application is all about rewriting the program itself. But actually rewriting is only a small fragment of efforts needed. For

People tend to think migrating an application is all about rewriting the program itself. But actually rewriting is only a small fragment of efforts needed. For some large organizations the legacy code base is so large that it would be crazy to rewrite them in a different language in the first place. This does not event mention the effort to test or validate if the new application works as expected. Put those thing aside, building a new infrastructure with PC servers and hire/retrain the operations would almost much larger than anticipated by most of the people. After evaluating all the options, scale up/out with MFs would be the cheapest and most reliable solution to provide more capacity for a perfectly working application. IBM has done a decent job on keeping MF backward compatible. There are lots of core banking systems running S360 Assembly applications on latest MFs today, in comparison, COBOL is not that old at all.