Complex sentence: In March 2011, the 16:9 resolution of 1920 × 1080 became the most commonly used resolution among Steam users; the previous most common resolution was 1680 × 1050 (16:10).
Split into simpler sentences: In March 2011, the 16:9 resolution of 1920 × 1080 became the most common used resolution among users of Steam. The earlier most common resolution was 1680 × 1050 (16:10).