Ignoring screen size for the moment, when comparing a monitor that is 1920 x 1080 (16:9 ratio) to a monitor that is 1920 x 1200 (16:10 ratio), the monitor that is "1080" will have 10% less vertical lines of pixels (120 of them) than the monitor that is "1200". Additionally, assuming the two monitors to have exactly the same diagonal dimension and that the pixels are exactly square (not always quite true), the "1080" monitor would be very slightly wider and somewhat less tall than the "1200" monitor.
Specifically, assuming both monitors to have exactly 22-inch screens, measured diagonally, and, again, assuming the pixels to be exactly square, you would have:
- A 1920 x 1080 monitor whose screen would be 19.175 inches wide by 10.786 inches tall, 206.813 square inches and 10,026.45 pixels per square inch; or,
- a 1920 x 1200 monitor whose screen would be 18.656 inches wide by 11.660 inches tall, 217.528 square inches and 10,591.74 pixels per square inch.
Essentially, the "1080" monitor would appear very slight larger (because of its extra ~ 1/2-inch width), less tall (because of its lacking ~ 7/8-inch height), and would have slightly less resolution (because of its pixel density per square inch).
Practically, there is very little difference between the two. The biggest loss using the "1080" monitor would be of a few extra lines of text at the bottom of the screen (those 120 vertical pixels' worth) while surfing the internet, doing word processing, or working with spreadsheets. For gaming and watching multimedia material, the differences are negligible. And, typically, "1080" (16:9) monitors are slightly less expensive than "1200" (16:10) monitors.
Edited to add: With a 24-inch diagonal, the "1080" screen would be about 0.6-inch wider and about 1-inch shallower than its "1200" counterpart. Again, the resolution differences between the two are negligible -- the only significant difference is that extra 120 lines of pixels with the "1200" screen monitor. And the price differential.
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