Mainframe

What is it

A mainframe is a large-scale computer built for three things: running without interruption, processing very high transaction volumes, and doing so with high levels of security and reliability. IBM defines it as a large, high-performance computer designed for continuous operation and high-volume transaction processing.

For a manager: when you pay by card, check a balance, or a large payroll is processed, a mainframe may be involved somewhere in the chain.

A Mainframe Is Not an “Old Server”

It’s a common mistake to think of mainframes as abandoned technology. IBM keeps building new generations: as of this entry, the latest is IBM z17, with the Telum II processor aimed at accelerating AI workloads. There’s also the LinuxONE line, designed to run Linux and containers on the same hardware family.

What’s usually “old” isn’t the hardware but the applications running on it: COBOL programs written decades ago, with little documentation and concentrated knowledge.

Typical Components of the Mainframe World

Component	What it does
z/OS	IBM’s mainframe operating system; handles transactions and batch jobs at the same time
CICS	Online transaction manager (for example, operations from a digital channel)
IMS	Combines a hierarchical database with transaction management
Db2	IBM’s relational database
JCL	Language for defining and scheduling batch jobs
COBOL	The language much of the business logic is written in

Digital channels (app, web, ATMs)
            ↓
     [APIs / middleware]
            ↓
┌───────────── MAINFRAME ─────────────┐
│  CICS (online transactions)         │
│  COBOL programs (business rules)    │
│  Db2 / IMS (data)                   │
│  Nightly batch (JCL)                │
└─────────────────────────────────────┘

Why It Matters for Companies in Latin America

Organizations in the region that automated their large-scale operations on a mainframe face common questions today:

Cost: licensing, capacity, and support contracts weigh on the IT budget
Talent: it’s increasingly hard to find COBOL, CICS, or JCL specialists
Speed: digital channels demand weekly changes, but the core changes quarterly
Integration: connecting the core to cloud services, analytics, or AI

Strategies for the Mainframe

There’s no single answer. AWS’s migration guide, for example, lists mainframe applications among those that require careful assessment and planning before being moved.

Strategy	What it involves
Retain and integrate	Keep the mainframe and expose its transactions through APIs
Rehost	Move applications to environments that emulate the mainframe, with minimal changes
Refactor / rewrite	Reimplement the logic in modern architectures, such as microservices
Incremental hybrid	Extract domains one by one with the Strangler Fig pattern

These options map to the migration “Rs” explained in Rehost, Replatform, Refactor.

Common Mistakes

❌ Deciding to leave the mainframe based only on license costs → You must add the cost and risk of migrating, testing, and operating the new platform

❌ Forgetting batch → Nightly job chains and their dependencies are often the most complex part

❌ Migrating without equivalence tests → Financial calculations must produce exactly the same result on both systems

Practical Example (illustrative)

A bank wants to launch a product lookup app without touching its mainframe core:

Balance and transaction lookup operations are exposed as APIs
The app and web portal consume those APIs through an API gateway
A read replica of the data is created in the cloud for analytics
Over time, lower-risk domains (for example, notifications) are reimplemented outside the mainframe

Evaluating what to do with your mainframe? At Nextsoft we support these projects together with specialized strategic partners: the partner carries out the migration and Nextsoft delivers new modules, integrations, frontend and QA. Check out the legacy system modernization service or let’s talk.

COBOL - The language of much mainframe software
Rehost, Replatform, Refactor - Strategies for migrating workloads to the cloud
Strangler Fig - Pattern for extracting functionality piece by piece
API - How to open the mainframe to digital channels
Microservices - A frequent target architecture when breaking up the core

Additional Resources:

IBM - What is a mainframe? - Definition and components
IBM Z - IBM’s current mainframe family
AWS - Migration strategies - The 7 Rs and how mainframe applications are treated

Pronunciation