Mainframe software is the software that keeps mainframes running, together with the tools that move applications off them. A mainframe is a large central computer that banks, insurers, airlines and governments have used since the 1960s for their most important records. Today, IBM makes almost all of the world's mainframes.
Why do mainframes still exist? They are very reliable, and they can process millions of records in one night's batch of work. Over fifty years, banks and insurers wrote their business rules into programs in COBOL, an old programming language. These programs work. Rewriting them is slow, expensive and risky, because a small mistake can change thousands of customers' balances.
A mainframe needs many kinds of software besides its operating system. One kind manages its databases. One kind monitors its health. Another schedules the night's batch jobs in the right order, a job done by workload automation. Developers need tools to write and test COBOL. And newer systems, such as mobile apps, need a way to read the mainframe's data. So some tools turn a mainframe program into a web service that other programs can call.
Mainframes are used mainly by large banks and insurers in the United States and Europe. Fewer Indian banks run their core banking systems on them. But many of the engineers who build and support mainframe software work in Pune, Bengaluru and Chennai.
Consider a large life insurer in the United States, whose six million policies are recorded on a mainframe. Every night, a COBOL batch job works out which premiums are due and which policies have lapsed. Mainframe software schedules the job, watches it, and reports any failure as a ticket in the IT service management (ITSM) software. The insurer now wants its mobile app to show each policy's current value. A mainframe tool turns the COBOL program that calculates this value into a web service. The app calls the service, and the mainframe replies within a second. The old program keeps doing its job.
The insurer also wants to move some work off the mainframe over the next few years. Here, migration tools help. They read the COBOL code and map which programs use which files. Some tools convert COBOL programs into a modern language such as Java. The old and new versions then run side by side, and their results are compared before the switch. Banks face the same task with their oldest core systems. That work is called core banking modernisation.
Mainframe software is often priced by how much of the mainframe's processing power the customer uses. So reducing the processing that each job needs also reduces the bill.