> An application that deployed 50 years ago and never updated would not run on 64-bit processors and would not be able to use the TCP/IP protocol suite. You ca

> An application that deployed 50 years ago and never updated would not run on 64-bit processors and would not be able to use the TCP/IP protocol suite. You can run legacy 24-bit mainframe apps on modern 64-bit mainframes fine. You can use legacy 3270 "green-screen" CICS mainframe apps over TCP/IP using CICS Transaction Gateway, with basically no changes to your CICS app. It's just that mainframe customers pay a lot for this convenience and stability.