How does the gateway know where to load or store configuration files (SD card or non-volatile RAM)?

When the PLX3x gateway boots it checks for an SD card. If an SD card is present it will load the configuration file stored on the SD card. If an SD card is not present than the gateway will load the configuration file from the non-volatile RAM in the PLX3x gateway.

Note: When downloading configurations to the gateway the same principal applies. If an SD card is present than the configuration will only be written to the SD card. If an SD card is not present than the configuration will be written into non-volatile RAM.