The loader acts as a wrapper for the official vcds.exe . Because official software checks for an encrypted chip inside a genuine cable, the loader "tricks" the software into recognizing a third-party cable (often based on or STM32F4 chips) as a licensed interface. Hardware Compatibility

To successfully set up VCDS 21.9 with a loader, users typically follow these steps to avoid software blocking or "bricking" the cable: VCDS 21.9 Installation Guide | PDF - Scribd

Known for being one of the last stable versions with reliable working Engine Security Access (code 22791) for certain modules. How the Loader Works

Most 21.9 loaders are designed specifically for ATmega162 , STM32F405 , STM32F407 , or STM32F429 based cables.