Mainframes process the majority of the world's critical transactions. Every time you use an ATM, book a flight, or file an insurance claim, there is a good chance a mainframe handled it. Yet for most engineers trained on cloud-native and distributed systems, the mainframe is a black box with an intimidating reputation.
It doesn't have to be. The concepts are learnable. The architecture is logical. The tooling has decades of production hardening behind it.
Mainframe Decoded is a structured series for engineers who work alongside mainframes, inherit mainframe systems, or simply want to understand what is actually running inside that data center floor tile. Each post assumes you are a competent engineer. None of them assume any prior mainframe experience.
Tier 1 — The Foundation
Start here. These posts build the mental model everything else depends on.
- Architecture: Mainframe
- Architecture: CICS
- Explained: COBOL
- Architecture: VSAM
- Architecture: DB2 on z/OS
Tier 2 — Batch and Jobs
The other half of mainframe workload. Most production shops run batch jobs overnight that process millions of records. These posts explain how that works.
Tier 3 — Security
Mainframe security is mature, granular, and unlike anything in the cloud-native world. One post covers the essentials.
Tier 4 — The Programming Model
How programs are structured, how they call each other, how they manage memory, and how they handle failure.
Tier 5 — Integration and Modernization
Mainframes rarely stand alone. These posts cover how they connect to the rest of your architecture, from async messaging to REST APIs.
Tier 6 — Operations and Observability
How mainframes emit telemetry, how operators monitor them, and what reliability means at mainframe scale.
Read the series from the beginning by starting with Architecture: Mainframe and following the tiers in order.
Written by Phee Jay.