Within a given series, all models use the same hardware, and the different WAN speed ratings are obtained through different licensing options. For example, both SD-WAN 400 models (the 400-002 and 400-006) use the same hardware, and a given appliance can be licensed either as a 2 Mbps appliance or a 6 Mbps appliance, but a SD-WAN 400 can not be upgraded to a SD-WAN 800, 1000, 2000, or 3000. The same is true of the other series.
The licensed bandwidth applies only to the sending direction, so a SD-WAN 400-002, rated at 2 Mbps in the sending direction, is appropriate for an ADSL link with a 12 Mbps/2 Mbps download/upload bandwidth.
In addition to differences in WAN bandwidth capabilities, the different series vary in CPU power, installed RAM, and installed disk capacity.
All models use solid-state drives instead of conventional hard drives for increased speed and reliability.