In addition to what the article itself talks about, there's a number of other memory knobs you can twiddle for various use cases.
Is the user expected to know about OS packages on it. Are they installing/updating software components by hand, so they know the OS version which runs in the box even, are they calling it a "server"? If the answer is yes, it not "embedded".
If they interact with the device as with an appliance (a dvd player, microwave, car infotainment center, some radio base station and so on), then it is embedded. It can still be an 8 core Xeon monster, but because of how it is serviced and used it, I think of it as embedded.
The data layer is usually hardware or C drivers which handle streaming data. This is simple and as basic as possible so it can be monitored and managed by the control layer.
Yep, lower level stuff was done in C, managed and connected by Erlang, which also talks to Postgres.
