M/PC is a concatenative operating system designed for the Varvara platform, drawing inspiration from Openfirmware. It addresses file management on systems that do not use a traditional file browser, instead relying on a command-driven interface based on postfix notation, where functions follow their operands. The system presents a single prompt at the top of the screen for command input, allowing users to execute operations such as retrieving file sizes, reading and writing files, moving and renaming files, and running ROM files. Files can also store reusable sequences of commands, which can be included in operations using a tilde prefix.
The operating system is designed for use without a keyboard, offering navigation and command execution primarily through directional controls. Users can navigate folders, scroll through stacks, evaluate selected symbols, and access directories or return to previous menus using designated controls. M/PC supports launching as a BIOS ROM on Varvara, enabling the system to return to the BIOS interface when a specific key is pressed rather than rebooting. Upon boot, it attempts to draw a wallpaper from an ICN file named according to the screen dimensions.
A comprehensive set of primitives is provided, including commands for directory listing, file movement, date and time retrieval, ROM execution, icon drawing, text file reading, file length calculation, file creation, content retrieval, copying, erasing, renaming, stack manipulation, arithmetic operations, hexadecimal and decimal conversions, concatenation, comparison, logical operations, screen resizing, console output, and system exit. These primitives are designed to be used in the postfix style characteristic of concatenative languages.
0 license, as indicated by the copyright notice spanning 2008–2026. The system is positioned as a tool for managing files and executing commands on the Varvara platform without reliance on graphical file browsers, making it suitable for users interested in alternative operating system paradigms or minimalist computing environments.
In the Frameworks & SDKs space, XXIIVV takes a focused approach. It focuses on providing a minimal, scriptable operating system for file management and command execution on Varvara devices. It is built as an open-source project for retrocomputing enthusiasts. XXIIVV is open source under the Open Source license. It runs on the web, Linux, Windows, and macOS.
XXIIVV builds and maintains XXIIVV, and the product first shipped in 2026. Key capabilities include postfix notation, file management, and command prompt.
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M/PC – A Concatenative OS verified by the PulseGate indexer
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