6, 8, and 21-pin
I noticed that the terms list doesn't mention pins. I think that as pin numbers are the main way for users to identify the type of DCC chip(s) they are using that it might be worth mentioning pins in an article to explain any differences between the 6, 8 and 21 pin systems. For example, Bachmann list all of their locomotives by DCC pin count, and it's pretty confusing! I'd write the article, but aside from 21-pin chip obviously not fitting an 8-pin socket, I've no idea what the differences are myself! -- 184.108.40.206 16:46, 6 August 2011 (EDT)
The number of pins is discussed under the NMRA connector topic.
Whether or not the locomotive or the decoder is equipped with an NMRA connector is another story. They may or may not, and decoders can be ordered with or without the connector. Twenty one pins is probably a JST connector. They are typically used to connect the PCB to the wiring harness.