The SoftDevice supports the use of a bootloader. A bootloader may be used to update the firmware on the System on Chip (SoC).
The nRF52 software architecture includes an MBR (see SoC application with the SoftDevice). The MBR is necessary for the bootloader to update the SoftDevice or to update the bootloader itself. The MBR is a required component in the system. The inclusion of a bootloader is optional.