Safe browser labs for critical enterprise skills

Mainframe learning, rebuilt for beginners.

Practise z/OS-style workflows, datasets, JCL job submission and spool output in a safe browser lab with Zed guiding you as you learn.

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app.mainframe101.org/dashboard/lesson/fundamentals-4

Fundamentals/Lesson 4: Your first commands

3 / 10

3270 TERMINAL

MAINFRAME101 MF/OS Version 2.5

────────────────────────────────────────────────

SYSTEM READY

> DISPLAY T

IEE136I LOCAL: TIME=14.23.45 DATE=2026.125

> DISPLAY IPL

IEE254I 08.15.30 IPLINFO 342

SYSTEM IPLED AT 08.15.30 ON 2026.118

RELEASE z/OS 2.5.0 LICENSE = z/OS

> DISPLAY M=CPU

STEP 3 / 10

The system responded instantly. That output follows real z/OS-style message conventions. IEE136I is the message identifier. Every message on z/OS has one. You will get used to them.

you

Why does it say 2026.125 instead of a normal date?

Julian date: year followed by the day of the year. Day 125 of 2026. Mainframes have used this format since the 1960s. Compact, unambiguous, and still everywhere in production.

›Ask Zed a question…

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Built for students, apprentices, developers and anyone starting their mainframe journey.

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Mainframe skills are valuable. Learning them is still too difficult.

Real mainframe learning often involves installs, credentials, VPNs, tooling, waiting lists and fragile environments. Mainframe101 removes the setup pain before it becomes a blocker.

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A safe mainframe lab in the browser.

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Simulated terminal

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Create, browse, and edit partitioned and sequential datasets the way you would on a live system.

JCL job submission

Write and submit JCL into the simulated job queue. See the job picked up, run, and end.

Spool output

Inspect JES spool messages, condition codes, and step output just as you would in SDSF.

USS-style files

Navigate and edit Unix System Services style paths alongside traditional MVS datasets.

Editable code members

Open, edit, and save COBOL, JCL, and REXX members directly in the browser.

Quizzes

Short knowledge checks embedded in every lesson confirm understanding before you move on.

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COBOL basics

Write, edit, and step through COBOL programs with syntax support and Zed explaining each clause as you go.

CICS transactions

Practise CICS commands and transaction flows in a simulated environment, without needing a live CICS region.

DB2 and RACF

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Write and submit JCL into the simulated job queue and see it picked up, run, and end.

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Inspect spool output, condition codes, and step messages. Ask Zed to explain anything you missed.

Zed

Meet Zed, your mainframe tutor.

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Zed

Fundamentals · Lesson 2: What is a mainframe?

Every time you tap your card at a checkout, a mainframe is likely involved in approving that transaction in milliseconds. 71 of the world's top 100 banks run on IBM Z. You're about to understand exactly why.

Why do banks still use them instead of modern servers?

Reliability. IBM Z systems are designed for 99.9999% uptime, around 31 seconds of downtime per year. Nothing else comes close. Banks cannot afford downtime, so they have never left.

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Built for the next generation of mainframe talent.

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Build a foundation in mainframe before entering the workforce.

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Get up to speed on z/OS without needing system access.

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Study mainframe concepts with no infrastructure overhead or waiting for system access.

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Learn the z/OS skills that power financial services before working on a real system.

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Move into mainframe from another discipline with a guided, hands-on starting point.

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Building in public

Built by a new mainframer, for new mainframers.

Mainframe101 is being built by Kyle Pressley to make mainframe learning easier to access, easier to practise, and less intimidating for beginners.

The goal is simple: remove the setup pain and help more people get hands-on with mainframe concepts from day one.

Be first to learn mainframes the modern way.

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