The Ramdisk enters the picture when the iPhone XR enters or DFU (Device Firmware Upgrade) Mode . In these states, instead of loading the full iOS kernel from the main storage, iBoot loads a compressed Ramdisk image (usually a .dmg or .img4 file) into the device’s 3GB of LPDDR4x RAM.
And for the developers and hackers still fighting to unlock the A12: keep digging. The Ramdisk is the key. iphone xr ramdisk