Complex sentence: Kay and Fran would conduct their work in a large, empty classroom on the first floor of the Moore School; the same room would later be the one where the ENIAC was built and operated until December 1946.
Split into simpler sentences: Kay and Fran would conduct their work in a large, empty classroom on the first floor of the Moore School. The same room would later be the one where the ENIAC was built and operated until December 1946.