Home / Comparisons / IDMS vs Db2
① Comparison · Databases
IDMS is a Broadcom (CA) network database. Db2 for z/OS is IBM relational. The gap between them is an application rewrite, not a data move, which is why the licensing decision usually beats the migration decision on cost.
Audit notice or renewal under 18 months out? We mobilize within 48 hours.
Get expert help →If your applications run reliably on Broadcom (CA) IDMS and perform, keep them and negotiate the IDMS renewal hard, because migrating to IBM Db2 for z/OS is an application rewrite measured in years, not a database swap, and it moves you onto Db2's own capacity bill rather than off the meter. Migrate to Db2 when the driver is strategic, a relational consolidation, a skills risk, or a platform direction already set, with licensing as one input among several. Choosing IDMS to Db2 purely to cut a software line is usually the expensive way to solve a problem that the renewal table can solve faster.
The two are different database paradigms that happen to share a platform. IDMS is CODASYL network, where applications navigate explicit record sets; Db2 is relational and set based, accessed through SQL. That architectural difference, not the data volume, is what makes the migration hard.
| Dimension | Broadcom (CA) IDMS | IBM Db2 for z/OS |
|---|---|---|
| Data model | CODASYL network, navigational | Relational, set based via SQL |
| Owner | Broadcom (CA) | IBM |
| Licensing | MSU capacity, Broadcom renewal and uplift exposure | MLC, sub capacity MSU via SCRT, Tailored Fit Pricing option |
| Application code | Navigational DML embedded in programs | SQL against a redesigned relational schema |
| Skills | Scarce and aging IDMS expertise | Broad relational and SQL skills base |
| Switching cost | Low to stay; the lock in is the lever vendors use | High to arrive; rewrite plus schema redesign |
| Main licensing lever | Negotiate the IDMS renewal and unbundle it | Optimize sub capacity and evaluate TFP fit |
Directional comparison. Confirm your IDMS entitlement on your Broadcom order and your Db2 metric on your IBM agreement; both are capacity based and both are negotiable.
The applications are stable, performant, and business critical, the IDMS expertise to run them is still in place, and the real problem is the renewal number rather than the technology. Here the win is on the contract: reconcile consumption, challenge the MIPS to MSU conversion, cap uplift, and pull IDMS out of any wider Broadcom bundle so it can be benchmarked. You keep a database that works and you take the cost down without a multi year program.
The direction is a relational consolidation, IDMS skills are a genuine continuity risk, or a broader modernization makes the rewrite worth funding for reasons beyond a single license line. If you go, scope the application rewrite and schema redesign with realistic numbers, plan the parallel run, and remember the destination is Db2's own sub capacity bill, so optimize that licensing from day one rather than inheriting an unmanaged Db2 footprint.
No. IDMS is a CODASYL network database where applications navigate explicit record relationships, while Db2 is relational and set based. The application code that walks IDMS sets has to be rewritten to issue SQL against a redesigned schema, so the migration is an application rewrite and a data model redesign, not a port. That is why IDMS to Db2 programs are scoped in years and why the difficulty lives in the application layer, not the data move alone.
Both are capacity based on the mainframe. IDMS is a Broadcom (CA) product, commonly licensed on MSU and exposed to Broadcom renewal uplift and the MIPS to MSU conversion question, and it is often bundled inside a wider Broadcom mainframe agreement. Db2 for z/OS is IBM monthly license charge software, billed on sub capacity MSU through SCRT and increasingly offered under Tailored Fit Pricing. The licensing question is not which is cheaper in the abstract but which renewal you are better positioned to negotiate.
Rarely on licensing cost alone. A migration that costs years of program spend to escape an IDMS line that could be renegotiated is a poor trade, and you would be moving onto Db2's own capacity bill, not off the meter. Migration makes sense when it is driven by skills risk, strategic direction, or the need to consolidate onto a relational platform, with licensing as one input. If the goal is purely to lower the IDMS bill, the faster path is usually to negotiate the IDMS renewal hard first.
Related comparison: keep vs exit. Related concept: the MIPS to MSU conversion question. Publisher hubs: Broadcom (CA) and IBM. Put it to work: Broadcom renewal advisory.