Why not a full length upper deck on a 747-600X

From:         tomas@medialab.ericsson.se (Tomas Stephanson)
Organization: Ericsson
Date:         17 Sep 96 02:24:43 
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I saw some pictures on the new proposed 747-600X and saw that the
upperdeck did not extend the whole length of the aircraft compared
to the Airbus 3XX.

Why does the 747 have a upper deck in the first place? Was it
for futre expansion?

Why does Boeing not want to extend the upperdeck the full length of
the aircraft, is it not economical, aerodynamic, weight penalty?