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 −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 by Boeing. However, 747-100s have been converted to freighters. A total of 167 747-100s were built.
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