The Aircraft
The E-4B is obviously a modified Boeing 747, or VC-25. It started out as a 747-200, but has had equipment added to make it an airborne command post. There was an E-4A, but these have been modified to B standard. The big visual difference between an A and a B is the fairly large hump on the top near the front. This houses the SHF SATCOM antenna.
The E-4B has a crew of 48 to 112, depending on mission needs. It can stay aloft for a week if necessary, the limiting factor being engine lubricants. In case of national emergency, the President, the cabinet, and whoever else is deemed necessary would be aboard.
The E-4B has not been upgraded to a glass cockpit, as the analog instruments are less susceptible to EMP (electromagnetic pulse) damage from a nuclear event.