Mainframe application developer
The person who writes and changes the business programs: COBOL, JCL, SQL and the logic that runs the organisation.
Also written COBOL developer, application programmer
An application developer on the mainframe writes and maintains the programs that do the organisation's work: calculating interest, processing claims, settling payments, producing statements.
Day to day that means reading existing code more than writing new code. A change usually begins with understanding a program that has been running for twenty years, finding where the rule you need to change lives, working out what else touches the same data, and making a narrow change that does not disturb anything around it.
The toolkit is COBOL for the logic, JCL to run it, SQL for relational data, and CICS commands for online work, with ISPF and the debugger as the working environment. Increasingly it also includes modern tooling such as IDEs, source control and automated pipelines, as sites modernise how the work is done rather than rewriting the applications themselves.
The valuable skill is not syntax. It is reading unfamiliar code accurately and understanding the business behind it, and that is what takes time to build.
Related terms
- COBOLThe programming language most business logic on the mainframe is written in. Verbose by design, and still running the world's payments.
- JCLJob Control Language: the language used to tell the mainframe what programs to run, in what order, and with what files.
- CICSThe transaction manager that runs online mainframe applications, and the software behind a great many screens bank staff use.
- DB2 for z/OSIBM's relational database on the mainframe, where a great deal of the world's banking and insurance data is stored.
- Legacy systemAn older system still doing essential work. On the mainframe, usually code that has been correct and running for decades.
- Production supportKeeping live systems running: diagnosing failures, fixing what broke, and getting the service back.