Passage: The first 747-100s were built with six upper deck windows (three per side) to accommodate upstairs lounge areas. Later, as airlines began to use the upper deck for premium passenger seating instead of lounge space, Boeing offered a ten-window upper deck as an option. Some early -100s were retrofitted with the new configuration. The -100 was equipped with Pratt & Whitney JT9D-3A engines. No freighter version of this model was developed, but many 747-100s were converted into freighters. A total of 168 747-100s were built; 167 were delivered to customers, while Boeing kept the prototype, City of Everett.

Question: What is the specification of the first 747-100s?
six upper deck windows (three per side)