In 1990 Andreas Kromke (the author of KAOS TOS, the heavily modified and performance-tuned TOS for the ST range) looked at TOS and said: one program at a time? No, thanks. Mag!X was born, later MagiC: a real multitasking OS for the Atari ST, with several GEM apps running side by side in their own windows, and still happy with software written for TOS. It was a commercial product for years. Then Kromke did something few authors do: he opened the complete sources under the GPLv3. And this year he shipped MagiC 6.30 for Atari computers. In 2026. On a 68000. Respect. Normally MagiC boots from disk: TOS starts first, then a loader pulls the kernel into RAM. We thought that was a waste of perfectly good RAM, so we built the MagiC ROM Builder. It turns MagiC 6.30 into a 256 KB ROM image that boots in place of TOS, plus the boot floppy or hard disk files for its desktop. Everything happens in your browser, nothing to install. Flash it with the SidecarTridge TOS Emulator on an STE or Mega STE, or on an ST or Mega ST with the 256KB Decoder. No TOS needed, around 240 KB more free RAM, and it boots straight into a multitasking desktop. Build your ROM: magic.sidecartridge.com/ MagiC sources by Andreas Kromke: gitlab.com/AndreasK/Atari-Ma…