Mainframe Back to the Future

By Tim Leader

With its unrivalled stability, security and power the mainframe has long offered enormous benefits to the global business community. But as well as this, resilience and business continuation are other major benefits the platform provides.

The following simple example demonstrating the ease with which an application written a generation ago can be ported to the latest modern mainframe environment without change is also well worth mentioning.

Back in 1986, I was asked to write a CICS application program to produce output to the POWER spool in order to test document formats used by some newly installed printers. The application was created using the CICS COBOL compiler under CICS version 1.6. The processor was an IBM 4341 running the VSE SP2.1 operating system. Once testing had been successfully completed, the code was stored away on VM CMS just in case it was ever needed again.

Fast-forward 36 years to 2022 (where did all those years go?!)

A requirement arose to demonstrate the creation of document output from a CICS application for an ongoing project.

I remembered that my 36-year-old CICS COBOL test application fit that bill exactly.  However, this requirement was not to run on z/VSE, it was needed to run on z/OS 2.5 under CICS TS 6.1 on a z15 processor. Being unsure whether any alterations were going to be required, I simply copied the COBOL source from the z/VSE job stream and pasted it directly into my CICS COBOL job stream to see if it would compile. Remember that no changes were made to the core COBOL application source code at all, the only difference between the two being the wrap-around Job Control and linkage parameters needed to run the compile.

I watched with interest as the compile and link completed in lightning-quick time without any compilation errors—the code was still valid; the new module was now ready to be tested! 

Next, the acid test—would this application first written so long ago on a completely different hardware platform, operating system and CICS version provide the desired results without abending? There was still that possibility of course.  So, I ran the process through CEDF (CICS Execution Diagnostic Facility) just for safety.

I needn’t have been concerned; the application completed without incident. And there on the JES output queue were the exact same print lines that were created on the VSE POWER queue so long ago…

With the constant advancement the new IBM hardware and software brings us, it’s comforting to know that applications written so long ago are still able to run successfully on today’s modern mainframe platforms. This is one of the reasons the mainframe is such a solid, dependable platform that continues to stand the test of time.

Long live the mainframe! 

Original article on the IBM Community website.

I am a member of the mainframe community. I am excited to join in on the conversation.