A flash file is the official, low-level software package designed specifically for a device's hardware. For the CPH1803, which runs on a Qualcomm Snapdragon 450 chipset, the flash file contains the bootloader, kernel, system partitions, modem configuration, and the recovery environment. Unlike an over-the-air (OTA) update, which only patches existing software, a flash file completely rewrites the phone's internal memory.
For the CPH1803, the flash file is required when: