BadWDSD is a hardware modchip for Sony PlayStation 3. By using Raspberry Pi Pico (RP2040), it is possible for non-CFW-compatible models to boot qCFW.
The modchip utilizes a quirk of the PS3's XDR DRAM, where by utilizing its WDSD serial register feature, custom data can be written to the memory very early in the boot process (in this case, when the system's bootldr [first bootloader] is decrypting lv0 [second bootloader]), thus allowing the end user to have lower level code execution on the system.
All the standard CFW functions are usable except dumping the EID root key and anything related to it, due to how the key is stored on the metldr2 memory, which is inaccessible without the flash patch used by standard CFW, and how Sony patched that exploit with metldr2 consoles (late CECH-25XX and newer). That being said, the ATA/ENCDEC keys can be dumped separately with BadWDSD, which still allows you to do HDD recovery without needing to dump the eid_root_key. DEX mode is also accessible in qCFW, so not having EID root key access doesn't matter on a qCFW system does not matter due to any exclusive features related to it still being achievable through alternative implementations.
All PS3 models that cannot install standard CFW are currently supported regardless of flash type.
For more instructions regarding the installation of the modchip and qCFW, please refer to the official GitHub repo