M/PC is a concatenative operating system built for the Varvara platform, drawing inspiration from Openfirmware. It eschews a file browser, relying instead on postfix notation to manipulate the file system.

File operations are driven by a compact set of primitives that push and pop symbols on a stack. CommandsHKs like len, cat, and cpy allow developers to query, concatenate, and copy files directly from the prompt, while mov changes the current directory without a GUI.

The user interface consists of a single prompt and a set of navigationalgul controls that can be cycled through using a joystick or a minimal keyboard. The OS can launch ROM images via run and return to the BIOS when the F4 key is pressed, with the boot image uxnemu loading m_pc.rom or orca.rom.

M/PC’s lightweight footprint and stack‑based design make it ideal for embedded systems that need a reliable boot ROM and quick file manipulation without the overhead of a full desktop environment. The built‑in wallpaper loader draws WWx HH.icn, using screen dimensions encoded in hexadecimal to position graphics precisely.