I remember using two 17" displays side by side years ago (easily 9 years), now I've got two 27" 5K displays side by side. The difference is breathtaking!
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There's no difference in height. I'm looking at my old 24" on the desk next to my 27" and if there's any height difference it's on the atomic scale.
Since aspect ratio has changed from the days of the 24" display (from 16:10 to 16:9), height in proportion to width has changed. Since today's 27" are essentially the same height as yesterday's 24", it stands to reason that today's 24" will be shorter.
Early 2009 20-inch iMac - 1680 by 1050 (1.6:1)
Height: 18.5 inches (46.9 cm)
Width: 19.1 inches (48.5 cm)
Depth: 7.4 inches (18.9 cm)
Weight: 20 pounds (9.1 kg)1
Early 2009 24-inch iMac - 1920 by 1200 (1.6:1)
Height: 20.5 inches (52.0 cm)
Width: 22.4 inches (56.9 cm)
Depth: 8.1 inches (20.7 cm)
Weight: 25.4 pounds (11.5 kg)1
Late 2015 21.5-inch iMac - 1920‑by 1080 (standard - 1.77:1) 4096-by-2304 (Retina 1.77:1)
Height: 17.7 inches (45.0 cm)
Width: 20.8 inches (52.8 cm)
Stand depth: 6.9 inches (17.5 cm)
Weight: 12.5 pounds (5.68 kg)2
Late 2013-Late 2015 27-inch iMac - 2560-by-1440 (standard - 1.77:1) 5120‑by‑2880 (Retina - 1.77:1)
Height: 20.3 inches (51.6 cm)
Width: 25.6 inches (65.0 cm)
Stand depth: 8 inches (20.3 cm)
Weight: 21 pounds (9.54 kg)2