Vegetaco/ That is really irrelevant becuase the the diagonal length isnt fixed.
Someone who buys a 21" monitor today will not get the same real estate as an older 21" monitor. That is a fixed diagonal length. When comparing the standard sizing parameter manufacturers use to sell monitors, the consumer gets more for their inches when buying a 16:10 ratio monitor, more still when buying an even older 4:3 ratio monitor at 21".
How is that irrelevant? Manufacturers are still selling the same 21", 24", 30" monitors they did a few years ago, but the screen areas are smaller than their older, closer-ratio counterparts.
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Here's what Wikipedia says on the subject:
Industry moves away from 16:10 in 2008 to 16:9
Around 2008-2010, there was a rapid shift by computer display manufacturers to the 16:9 aspect ratio, and by 2011, 16:10 had almost disappeared from new mass market products.
The primary reason for this move is considered to be production efficiency.[3][6] Since display panels for TVs use the 16:9 aspect ratio, it's more efficient for display manufacturers to produce computer display panels in the same aspect ratio as well.[7] A 2008 report by DisplaySearch also cited a number of other reasons, including the ability for PC and monitor manufacturers to provide higher resolutions and diversify their products, "stimulating the growth of the notebook PC and LCD monitor market".[2]
The shift from 16:10 to 16:9 has been met with a mixed response. While the lower cost of 16:9 computer displays, along with the convenience of having the same aspect ratio in different devices, has been seen as a positive,[3] some consider 16:10 more suitable for productivity-oriented tasks, such as editing documents or spreadsheets and using design or engineering applications.[8][9]