Start with the workload, then qualify the provider
Mainframe modernization can retain and improve workloads, expose them through interfaces or move selected capabilities to another runtime. Migration changes execution location. Modernization can also happen on the mainframe. The provider must explain which outcome it proposes for each workload.
IBM Consulting publishes services for assessment, refactoring, mainframe application change and distributed or cloud targets. Kyndryl publishes mainframe services spanning modernization and operations. These companies are interview candidates based on published scope, not an independent ranking or a claim about the team available for your engagement. Ask each to demonstrate the same representative workload and disclose the products and subcontractors involved.
Verify more than COBOL translation
| Workload element | Evidence to request |
|---|---|
| COBOL or PL/I | Supported dialects, compiler behavior and conversion exceptions |
| JCL and batch | Job graph, restart points, schedules and downstream file consumers |
| CICS or IMS | Transaction boundaries, state and failure behavior |
| Db2 or VSAM | Access patterns, record layout, keys and reconciliation rules |
| z/OS operations | Security integration, deployment, monitoring and operator procedures |
Include third-party utilities, copybooks, packed-decimal representations and business rules outside the source modules. A provider's language list does not establish that a converted workload will complete the batch window or preserve an integration's file contract.
Download the evaluation worksheet and record the owner, evidence and decision for each row. Its review fields are blank; it is a reusable template, not a completed assessment.
Compare retention, rehosting and refactoring
Retain and extend when the platform continues to meet the core requirement and an interface or delivery change removes the constraint. Rehost when preserving much of the implementation on a compatible target is justified. Refactor or convert when the target requires a different implementation and the behavior can be verified. Replatforming and offloading should name exactly which runtime or processing responsibility changes.
For a hybrid design, map the calls and data crossing the platform boundary. Moving one step out of a batch chain can create new latency, failure and operating dependencies. A COBOL-to-Java demonstration is only one part of an application-level transition.
Assess the dependency graph before extrapolating
Request an inventory of programs, transaction entry points, datasets, jobs, schedules, interfaces and owners. Include execution evidence because static analysis may not reveal conditional or operational dependencies. Classify conversion exceptions and unsupported components before calculating the next wave.
Choose a proof of concept containing a difficult representative path, rather than a small isolated program. Record what remains untested. Feasibility should include access to data, domain specialists, target operations and the ability to reproduce outputs under a controlled baseline.
Define equivalence and cutover evidence
Compare business transactions, batch totals, record-level differences, exception behavior and required timing. Decide which differences are intentional and who accepts them. Functional equivalence is a claim to test against the agreed scope. It is not established by successful compilation.
A parallel run needs a rule preventing duplicate effects and a reconciliation process for late changes. Test batch restart, partially completed transactions and a failed downstream dependency. Record authoritative data ownership, cutover approval and the latest state from which rollback remains valid. A target that runs a sample transaction still needs workload and batch-window evidence before production acceptance.
Compare the full operating obligation
Include assessment, manual conversion, test-data preparation, target capacity, licenses, parallel operations, training and retirement. Confirm which licenses continue after migration and which depend on another supplier's runtime. A code-size estimate does not cover the cost of undocumented behavior or target support.
The RFP should request named specialists, a pilot acceptance packet, customer participation, a skills-transfer plan and an exit procedure. Ask how your staff can maintain the result after proprietary conversion tooling is no longer available. Separate an infrastructure-hosting contract from application acceptance and ongoing engineering.
Verify the exact platform and tool engagement
For AWS, Azure or an IBM-centered target, ask for current platform documentation and confirmation of any claimed partner designation. A badge or ecosystem listing is a qualification input, not evidence of your workload's equivalence. Automated and AI-assisted conversion still need independent tests, reviewable exceptions and private-code handling terms.
Compare tools with tools and service commitments with service commitments. This guide does not publish a benchmark of AI models, a conference directory or a market-size ranking. Its acceptance matrix can be reused regardless of which provider or target you interview.
Sources
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