Mainframe modernisation
Mainframe modernisation without the leap of faith.
Modernise COBOL workloads in small, verified steps, with evidence your board, auditors and regulators can follow.
- 01What mainframe modernisation means
- 02Where programmes go wrong
- 03Montora's approach: modernise in verified steps
- 04Built for regulated industries
- 05Works alongside the plan you already have
In short
- Mainframe modernisation (or modernization) means moving workloads off ageing mainframe platforms and code, usually COBOL, onto modern languages and infrastructure.
- Most programmes fail on proving equivalence, not on writing new code.
- Montora modernises in small steps, replays recorded legacy behaviour against every change and keeps a person as the final gate.
What mainframe modernisation means
There are four broad routes: rehost the same code on new hardware, replatform it onto a new runtime, refactor it into a modern language, or rewrite it from the requirements. Each trades speed against how much you change. Our guide compares the main mainframe modernisation approaches.
Whatever the route, the question at cutover is the same: does the new system do exactly what the old one did?
Where programmes go wrong
Large migrations rarely fail because the new code can't be written. They fail because nobody can show it behaves the same before the switch. In 2022 the UK's FCA and PRA fined TSB £48.65m over its 2018 IT migration, citing failures in planning, governance and outsourcing risk.
The knowledge problem compounds it: the people who wrote the programs have often retired, and the business rules live only in the code.
Montora's approach: modernise in verified steps
Montora maps the estate, then migrates one reviewed piece at a time. Every change is replayed against recorded runs of the legacy system, divergences are flagged with the exact field and account, and nothing merges without a person's approval.
The output of each step is code plus evidence: what was compared, what matched, what was overridden and by whom.
- Incremental, dependency-ordered migration instead of a big-bang cutover
- Replay-based migration testing on every change
- Business rules drafted for your experts to confirm
- Signed, reproducible evidence for risk, audit and model-risk teams
Built for regulated industries
Banks and insurers have to show their regulators that a change of system did not change outcomes for customers. Montora is designed around that obligation: evidence first, human sign-off always, and a record that can be verified without trusting the vendor.
Works alongside the plan you already have
Replay compares behaviour, not authorship. The same check that verifies Montora's own migrations can be pointed at code produced by another tool, a systems integrator or your own team. Talk to us about where it fits in your programme.
Questions
What is mainframe modernisation?
- Mainframe modernisation (also spelled modernization) is moving applications that run on mainframes, usually written in COBOL, to modern languages, platforms or cloud infrastructure, while keeping their behaviour the same.
What is the difference between rehosting and refactoring a mainframe?
- Rehosting runs the same COBOL on new infrastructure through an emulation layer, so behaviour barely changes but the code stays COBOL. Refactoring translates it into a modern language such as Java, which is more valuable long-term and is proven equivalent by replaying the legacy system's recorded behaviour against the new code.
How does Montora reduce mainframe migration risk?
- By working in small steps, replaying recorded legacy behaviour against every migrated change, flagging each divergence field by field and requiring a person to approve every change before it merges.
Can Montora check a migration done by another vendor?
- Replay compares the behaviour of the new code with recorded runs of the old system, regardless of who wrote the new code. Talk to us about your programme.
Sources
Related
Bring one system. We'll show you the proof.
Montora is taking on a small number of design partners: banks, insurers and other teams with COBOL they can't afford to get wrong.