People are giving you software answers, but I think the answer is actually about hardware. Monitor manufacturers realized they could brand their screens as "108

People are giving you software answers, but I think the answer is actually about hardware. Monitor manufacturers realized they could brand their screens as "1080p HD" to match them up to the TV marketing pitch. Why bother trying to make a screen with 1600 vertical pixels when you can just use that magic word, 1080p?