To what extent is the HOST system still in use? 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.
From this news article dated April 30, 2015:


  "As of today, Host is history," FAA Administrator Michael Huerta declared during a press conference.


From the latest NextGen report dated June 2016:


  In March 2015, the 20 planned ERAM sites achieved operational readiness, which signified the full commissioning of ERAM into the NAS and allowed the FAA to begin decommissioning the legacy HOST system.


So, it is fully out, it is not available as back-up, and no ATC system uses Host.