The Host Computer System (HOST) used to be the backbone of the US air traffic control centers (ARTCCs). There was a lot of publicity early in 2015 about the En-Route Automation Modernization (ERAM) fully replacing it, as the FAA announced they were finally finished implementing ERAM. However, deep in the FAA website, the HOST system still seems fairly active.
I just want to clarify if it is fully out now. Is it still available as a backup? Do certain ATC systems still draw from HOST systems? Do controllers still use certain HOST systems?
Overall this is a pretty technical question, but any information is helpful.