IMS Tutorial: The Complete Guide to IBM IMS Programming (2026)
IMS Tutorial: The Complete Guide to IBM IMS Programming (2026)
IBM IMS is one of the most enduring and commercially important database systems in enterprise computing. Introduced in 1968, IMS has processed the world's most critical transactions — banking withdrawals, insurance claims, healthcare records, and government benefit payments — every day for over 50 years. Organisations that depend on IMS are not migrating away from it: they are maintaining, extending, and modernising it.
For developers entering the mainframe field, IMS programming is one of the highest-value skills available. The talent pool is contracting through retirement, demand remains high, and the learning resources are sparse. This tutorial provides the complete IMS curriculum across 22 modules — from IMS fundamentals and hierarchical database design through DL/I programming, IMS Transaction Manager, and production administration.
What Is IMS?
IMS (Information Management System) is IBM's hierarchical database and transaction processing system for z/OS mainframes. It has two major components:
IMS DB (Database) stores data in a tree-shaped hierarchy of segments. Instead of rows and columns in tables, you have parent and child segments in a defined hierarchy. A root segment is the top of the tree; dependent segments hang below it. The database structure is defined in a DBD (Database Description), and access is controlled by a PSB (Program Specification Block) containing PCBs (Program Communication Blocks).
IMS TM (Transaction Manager) handles online transaction processing — receiving messages from terminals or other systems, routing them to MPP (Message Processing Program) regions, and managing the response. IMS TM competes with CICS in the mainframe transaction processing space, and many shops run both.
Data access is performed through DL/I (Data Language/I) calls from COBOL programs — function codes like GU (Get Unique), GN (Get Next), ISRT (Insert), DLET (Delete), and REPL (Replace), combined with SSAs (Segment Search Arguments) that filter and navigate the hierarchy.
Why IMS in 2026?
Proven at scale. IMS has processed critical enterprise transactions continuously since 1968. The throughput, reliability, and recovery capabilities of IMS are not matched by newer systems for the workloads it was designed for.
Irreplaceable installed base. Major banks, insurance companies, and government agencies run IMS applications representing decades of accumulated business logic, regulatory compliance controls, and operational tooling. The cost and risk of replacing these systems is prohibitive. IMS will be running production workloads well into the 2030s.
Structural talent shortage. The average IMS developer in production is in their mid-to-late career. Retirements are outpacing new entrants into the IMS skills pipeline, creating persistent salary premiums for developers who invest in this skill. IMS DBAs at Tier 1 financial institutions command $130,000–$185,000 in the United States.
How This Tutorial Is Organised
The 22 modules are divided into 5 phases. Work through them in sequence if you are new to IMS. Modules 1–4 (IMS Foundations) and Modules 10–15 (DL/I Programming) are the critical path — everything else builds on those foundations.
Phase 1: IMS Foundations
The Foundation phase covers what IMS is, how it differs from relational databases, its internal architecture, and the hierarchical data model that underpins everything.
Module 1 — What is IMS? IBM Information Management System Introduction The history, purpose, and real-world use of IMS in banking, insurance, healthcare, and government. The starting point for every IMS learner — explains why IMS still matters and what you will learn to do.
Module 2 — IMS Architecture: Regions, Address Spaces, and Components How IMS is structured internally — control regions, DLI regions, BMP regions, and how IMS manages databases and message queues on z/OS. The mental model you need before writing code.
Module 3 — IMS vs DB2: When to Use Each on z/OS Mainframe A practical comparison of IMS hierarchical databases and DB2 relational databases. Strengths, limitations, and when each is the right choice for enterprise workloads.
Module 4 — IMS Hierarchical Data Model Explained with Examples How IMS stores data in a tree-like parent-child hierarchy — root segments, dependent segments, and navigating hierarchical relationships. The conceptual foundation for all database design and DL/I programming.
Phase 2: IMS Database Design
The Database Design phase covers the artefacts that define an IMS database: DBDs, PSBs, PCBs, access methods, and secondary indexes.
Module 5 — IMS DBD: Database Description Complete Guide Writing and understanding IMS Database Description macros — DBDGEN, segment definitions, field definitions, and DBDLIB generation. The DBD is the schema for an IMS database.
Module 6 — IMS Segments and Fields: Designing the Hierarchy How to design IMS segment layouts, field definitions, key fields, sequence fields, and best practices for hierarchical data modelling that performs well in production.
Module 7 — IMS Access Methods: HSAM, HISAM, HDAM, HIDAM Explained The four IMS access methods — sequential (HSAM, HISAM) and direct (HDAM, HIDAM). When to choose each, performance implications, and how the access method affects DL/I retrieval patterns.
Module 8 — IMS PSB and PCB: Program Specification Block Complete Guide Defining Program Communication Blocks, sensitivity levels, processing options, PSBGEN, and how PCBs control which segments a program can access and how.
Module 9 — IMS Secondary Indexing: Complete Guide with Examples How IMS secondary indexes work — XDFLD definition, index databases, pointer segments, and using secondary indexes for alternate access paths to the same data.
Phase 3: DL/I Programming
This is the heart of the course. The DL/I Programming phase covers everything you need to write production COBOL programs that read and modify IMS databases.
Module 10 — IMS DL/I Calls: GU, GN, GNP Retrieval Commands The three core IMS retrieval calls: Get Unique (GU) for direct retrieval, Get Next (GN) for sequential scanning, and Get Next within Parent (GNP) for scanning child segments. Complete COBOL examples.
Module 11 — IMS DL/I ISRT, DLET, REPL: Modifying IMS Data Insert, delete, and replace segments in an IMS database using ISRT, DLET, and REPL calls. The rules for each operation — what must be retrieved first, position requirements, and status code handling.
Module 12 — IMS SSA: Segment Search Arguments Complete Guide Writing unqualified and qualified SSAs, command codes, boolean operators, and how SSAs control segment selection in DL/I calls. SSAs are the equivalent of SQL WHERE clauses in IMS.
Module 13 — IMS COBOL Programming: Your First DL/I Program Step-by-step guide to writing a COBOL program that uses DL/I calls — PCB mask definition in the Linkage Section, entry linkage, CALL DLI syntax, and status code handling patterns.
Module 14 — IMS Qualified SSAs and Boolean Operations Advanced SSA techniques — qualified SSAs with relational operators, multiple qualifications, boolean AND/OR logic, and nested SSA patterns for complex retrieval conditions.
Module 15 — IMS Cursor Positioning and Sequential Retrieval How IMS maintains position in the database hierarchy, sequential retrieval patterns with GN and GNP, and resetting position with GU calls. Essential for writing programs that process sets of segments.
Phase 4: IMS Transaction Manager
This phase covers IMS TM — the online transaction processing side of IMS — including MPP programs, MFS screen design, BMP programming, and Fast Path.
Module 16 — IMS TM Architecture: Message Processing and MPPs IMS Transaction Manager architecture — message queues, MPP regions, transaction routing, and how IMS TM handles online transactions from terminals and other systems.
Module 17 — IMS MFS: Message Format Service Complete Guide Designing 3270 terminal screens with IMS MFS — MSG, FMT, DEV macros, MFSGEN, and using MFS to format input and output messages for online IMS applications.
Module 18 — IMS BMP: Batch Message Processing Programs Writing IMS BMP programs that access both IMS databases and message queues in a batch environment — use cases, JCL requirements, and programming patterns for mixed batch-online workloads.
Module 19 — IMS Fast Path: DEDBs and MSDBs Explained IMS Fast Path for high-throughput applications — Data Entry Databases (DEDBs), Main Storage Databases (MSDBs), and Fast Path DL/I calls used in the highest-volume financial transaction environments.
Phase 5: Administration and Career
Module 20 — IMS Utilities and Recovery: Complete Operations Guide Essential IMS utilities — database backup and recovery, image copy, reorganisation, and disaster recovery procedures for production IMS environments.
Module 21 — IMS Performance Tuning and Monitoring IMS performance analysis tools, buffer pool tuning, OSAM vs VSAM considerations, database reorganisation, and common bottleneck fixes for production IMS systems.
Module 22 — 50 IMS Interview Questions and Answers (2026) The 50 most common IMS interview questions covering architecture, DL/I programming, DBD/PSB/PCB, access methods, TM, and administration — with full answers for mainframe job preparation.
IMS vs DB2: Which Should You Learn First?
If your goal is to work as a mainframe application developer, the answer is usually both — and most production environments use them alongside each other. But if you must choose an order:
Learn DB2 first if you already know relational databases (MySQL, PostgreSQL, SQL Server) and want to build on that foundation. DB2 SQL is familiar; the mainframe context adds z/OS specifics, embedded SQL in COBOL, and EXPLAIN-based performance work.
Learn IMS first if your employer or target employer specifically uses IMS, or if you are joining a team where IMS is the primary data store. IMS DL/I programming has a steeper initial learning curve than DB2 SQL, but the salary premium at IMS shops is often higher.
The IMS vs DB2 comparison module covers this decision in depth, with guidance based on the specific enterprise context.
Prerequisites: What You Need Before Starting
Required: A working knowledge of COBOL is strongly recommended before starting Phase 3 (DL/I Programming). DL/I calls are made from COBOL programs using CALL DLI statements — the PCB mask, Linkage Section linkage, and status code handling all assume you can write COBOL. If you are new to COBOL, start with the COBOL Mastery Course first.
Helpful but not required: Basic familiarity with z/OS concepts (JCL, datasets, JES2/JES3) is helpful for the administration modules, but not required for the programming phases. You can learn these in parallel.
Not required: You do not need access to a mainframe or IMS system. IBM's free Z Xplore platform provides cloud-based z/OS access including IMS.
What You Can Do After This Tutorial
Working through all 22 modules prepares you to:
- Write production DL/I programs — GU, GN, GNP, ISRT, DLET, REPL with correct PCB mask linkage, SSA construction, and status code handling for the full range of IMS access patterns.
- Design IMS databases — DBDs with full segment hierarchies, field definitions, HDAM/HIDAM access methods, and secondary indexes for alternate retrieval paths.
- Build IMS TM applications — MPP programs, MFS screen formats, and BMP programs for mixed online-batch workloads using IMS Transaction Manager.
- Work with IMS Fast Path — DEDBs and MSDBs for the highest-throughput IMS workloads found in financial services environments.
- Administer IMS — image copies, database recovery, utility execution, and performance tuning for production operations.
Ready to go deeper?
The IMS Mastery Course structures all 22 modules into a guided learning path with phase-by-phase progression — from your first DL/I call to Fast Path, MFS screen design, and IMS performance tuning.