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Release notes

What's new in MF/OS.

MF/OS is the simulated mainframe you work on inside Mainframe101. Here's what changed in it, in its subsystems, in Career Mode and in Zed, from your side of the screen.

September 2026

1 to 16 September 2026

Private beta

Zed can now see your machine, stories are read aloud, and MF/OS gains split screen, undo and far more capable REXX.

Added

  • ZedZed can see your machine. Ask why a job failed or where a file went, and he looks at your datasets, jobs and output instead of asking you to paste them.
  • ZedZed helps without doing the work for you. He nudges first, gives more if you ask again, and only hands over the answer when you tell him you are stuck.
  • ZedWhen you ask Zed to show you something, he can offer to open a member, a dataset or a job's output. You click to open it.
  • ZedZed remembers where you are in the career, and your conversations with him are saved per story and per system.
  • Career ModeStories are read aloud, with each word lighting up as it is spoken. Choose the narrator, pause with Space, and turn a quiet datacentre hum on or off.
  • Career ModeThe ZedBank career is open from your first morning onwards: set up your workspace, submit your first job and load the first customers.
  • ISPFSplit screen works. F2 opens a second screen and F9 swaps between them, so you can leave an edit half done and come back to it.
  • MF/OSUNDO. In the ISPF editor it steps back through your changes. At the READY prompt it tells you which command reverses what you just did, or that nothing can.
  • REXXREXX execs can do real work: stems, arithmetic, arguments, reading and writing files, and adding users and groups in bulk.
  • WorkbenchThe editor shows a column ruler and field labels on data files, and Tab jumps to the next field in a fixed-width record.
  • Career ModeCertifications show where each one is earned. An earned certificate opens as a document you can download or share to LinkedIn.
  • Career ModeTwo ways out if you get into a tangle: reset a forgotten sign-on password, or start the career again from the beginning.

Improved

  • Career ModeSteps are checked on what is actually on your machine, and if you are stuck after the hints there is always a way to move on.
  • RACFSecurity commands now stop and tell you when a value is missing or a keyword was ignored, instead of quietly doing something else.
  • Career ModeThe roadmap is split into chapters, a story you have started says Continue, and you can restart a story from the roadmap.

Fixed

  • WorkbenchPasswords with lower-case letters now work when you log on in one line.
  • A brief connection drop no longer signs you out, and your chosen colour no longer flashes to the default when a page loads.

August 2026

Private beta

Mainframe101 becomes a career: you are hired at ZedBank, learn through stories with Zed beside you, and grow the bank as you go.

Added

  • Career ModeCareer Mode. You start with a job offer at ZedBank, spend your first morning at the bank, and take on real work from there.
  • Career ModeStories replace lessons. Zed talks you through each idea while you do it, asks you questions, and replies to the answer you picked.
  • Career ModeYour own customers. Names you choose go into the bank as real records, and the bank grows as you finish work.
  • Career ModeNine certifications, one per subject. Each is earned by finishing its phase of the career and an unguided final story.
  • Career ModeReputation that rises as you complete work, shown on your dashboard.
  • Free RoamFree Roam: create, rename and remove your own systems, then open a terminal on any of them. Zed suggests one sensible next thing when you are not sure where to start.
  • MF/OSEvery system has a proper sign-on. You log on with a user ID and password, and a brand new system starts from a bare setup you bring up yourself.
  • An optional public profile page showing your rank, finished stories and certifications. It is off until you switch it on.
  • WorkbenchA keyboard reference for the terminal that opens the first time you arrive, and Zed points out shortcuts when they would save you typing.
  • Career ModeHover over a term in a story to see what it means, and flag any step that confused you.

Improved

  • WorkbenchPress Esc for the menu from anywhere, certifications open over whatever you are doing, and the story panel can be dragged wider or narrower.

Fixed

  • TSOLOGOFF now keeps you logged off after a page reload.

v1.0.0

31 July 2026

Private beta

The first release of the Mainframe101 lab: a guided path through the mainframe, in your browser, on MF/OS.

Added

  • Nine guided tracks inside ZedBank, from your first command through JCL, COBOL, DB2, CICS, RACF and REXX.
  • ZedZed, your mentor, who explains what is happening and why before showing you how.
  • WorkbenchA full workbench in the browser: datasets, the editor, live jobs and their output.
  • JESJobs wait their turn in a queue when others are running, and bigger jobs take longer to finish.
  • MF/OSA performance monitor whose figures come from the jobs you have actually run.
  • DB2DB2 tables are listed on their own in the explorer, separate from datasets.
  • Saved progress across every lesson, track and job, so you can pick up where you left off.
  • Certificates you earn and keep, as shareable digital credentials.
  • Voice mode, so lessons can be read aloud at your own pace.

Fixed

  • COBOLOverdrafts and loans show as negative balances, and keyed reads of indexed files work as written.

Try the latest build.

More lands every week. The public beta is open to everyone. Your desk at ZedBank is ready.

Start at ZedBank

Runs in your browser. Nothing to install.