Introduction: Why MEDOC 2.4 Still Matters In the fast-paced world of industrial automation, software evolves at breakneck speed. However, on the factory floors of small-to-medium manufacturing plants, legacy systems often run for decades. One such enduring piece of software is MELSEC MEDOC 2.4 —a DOS-based programming tool for Mitsubishi Electric’s MELSEC PLC (Programmable Logic Controller) family, including the venerable F, F1, F2, and K series.