PlasMa Mini-Mainframe Simulator

A simulator homage to old-school mini/mainframe systems with real lights and switches

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PlasMa simulates a complete mini/mainframe system in a self-contained desktop-sized box containing real lights and switches. The system comprises a simulated 'mini-like' processor with a small amount of main memory, and simulated 'mainframe-like' peripherals such as a paper tape reader and punch, mag tapes, exchangeable disks and an operators console.
The processor is 'micro-coded' and can run (currently) 3 different instruction sets; two based on the Princeton TOY architecture with 2K words memory for educational use, and a more advanced home-grown ISA based on NICE, with 64K words memory and floating point.
The simulation runs on an ATmega2560 MCU which also controls the user-interface comprising approx 540 LEDs, 100 switches, 6 SD-cards for the storage peripherals, LCD screen, keypad, speaker, Centronics interface for a dot-matrix printer, PS/2 interface for a qwerty keyboard... and a MIDI in & out interface for fun.

Here's part of an example video showing PI being calculated to 1000 decimal places, using 2 simulated mag tapes to process an array which is too big for main memory.

More details on the PhiliZound website.
Feel free to join in the discussions on the PlasMa Google group.

  • Feb-20 2024

    Phil Tipping02/20/2024 at 09:01 0 comments

    CoPEx - Cooperative PlaMa Executive

    Part 1 of an experimental executive program

  • Feb 2024

    Phil Tipping02/17/2024 at 09:38 0 comments

    Programming walk-through - 3-part video series

    Full walk-through of latest programming route using plasm assembler.

  • Dec 2023

    Phil Tipping12/22/2023 at 06:29 0 comments
  • Nov 2023

    Phil Tipping12/02/2023 at 16:18 0 comments

    Main memory increased from 2K to 64K words for the PleX ISA. This was part of an upgrade exercise using re-tracked PCBs, and was the final planned hardware change. Future updates will be firmware-only.

    Floating point functions added to PleX . This has not been rigorously tested yet, apart from running Lunar Lander :) but any fixes will only require firmware updates. 

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Phil Tipping wrote 01/27/2024 at 06:39 point

Feel free to join the discussions on the PlasMa Google group

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m.b. wrote 12/18/2023 at 12:56 point

When your in Germany, you can make your panels at, i have ordered my panels today, they ship whithin 3 Workdays. The Company accepts DXF Files, but you must "repair" the Files in a suitable Programm to get all Holes in the panels.

I importet the Front and Backpanel in the "Frontplattendesigner" from Schäffler ( ) an exported them again, so i was able to get the correct panels to order.

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Ale o co chodzi wrote 12/10/2023 at 16:24 point

nice but .... pdp11 is nice

or making normal cluster beowolf with 30 motherboards

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Phil Tipping wrote 12/11/2023 at 10:39 point

Agreed it would have been nice to emulate a real machine (the PleX ISA does use some ideas from the PDP series, such as the indirect, post-increment and pre-decrement addressing modes), but they would need a lot more work & research to emulate accurately... and real machines evolved over their lifetime so which variant would you emulate? 

I'm more interested in the hands-on experience and initial low-level software development such as bootstraps, executives, job schedulers etc. so didn't want to get bogged down making an accurate simulator of an existing machine, and then just running existing software packages. I think if you want to go this way, there are already many better simulators around.

Thanks for stopping by.

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Ale o co chodzi wrote 12/11/2023 at 14:38 point

If you are interested in modern versions of low-level computer components. I suggest you design a 10-12 bit computer from scratch. 8 bits is not much.
Run some standard os on it : fuzix, linux, minix, Serenity, dos, hurd etc.

We need new computers. But let them be energy efficient, or faster, or scalable like Parrallel's Epiphany.

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