When it comes to computer, TV, tablet or phone resolution and display most people just listen to the sales person they are buying from. Below is a small but important excerpt of a larger article that Gizmodo has written!
Screen Size: This spec sounds straightforward—it’s just the diagonal length of the screen. True, but that doesn’t actually tell you how big the screen really is. What really matters visually is the area of the screen (width times height) and that changes significantly faster than the diagonal size indicates, so you’ll either over or under estimate the true visual screen size based on just its diagonal size. To get an idea of the screen area, square the diagonal size (multiply it by itself on a calculator) and use that for comparison. For example, a 7 inch Tablet actually has less than half the area (49) of a 10 inch Tablet (100). The area also depends on the shape of the screen, which is another spec called aspect ratio (below). Lower aspect ratios have larger screen areas for the same diagonal size. For example, a 10-inch, 4:3 Aspect Ratio screen is 12-percent larger in area than a 10-inch, 16:9 screen. If you’re not handy with this math, you’ll often see the actual screen width and height listed in the specs. Just multiply them on your calculator to get the area.
16:9 and 4:3 Aspect Ratios: The aspect ratio is the screen width divided by its height and it’s the spec used to indicate the shape of the screen. It can be described as a ratio—like 16 by 9—or numerically by dividing the two numbers—1.78. For all consumer displays you can also get the Aspect Ratio by dividing the screen’s listed horizontal and vertical pixel resolution – dividing 1920 by 1080 is also 1.78. 16:9 is the standard aspect ratio for HDTV content, so it fits perfectly on 16:9 screens. While that’s often called “widescreen” most widescreen movies have aspect ratios much larger than 16:9, so you’ll see black “Letterbox” bars on the top and bottom of the screen, which reduces the effective viewable screen size and resolution. Another common aspect ratio is 4:3 or 1.33, which is also the same aspect ratio as content from 8.5 x 11-inch documents. This aspect ratio is better for reading in either Landscape or Portrait modes, but not as good for viewing widescreen content. The iPad has a 4:3 aspect ratio and the iPhone has 3:2 or 1.5. Other common aspect ratios are 5:3 or 1.67 and 16:10 or 1.6.
PPI Pixels Per Inch: As a result of Apple’s retina displays, pixels per inch is a very hot spec – it’s one of the most closely followed display Specs, but it’s also one of the most misunderstood. True, the higher the PPI the sharper the image on the screen, but what really matters is the sharpness perceived by your eye and that depends on the viewing distance from the screen (and also how good your vision is compared to 20/20 Vision). So PPI cannot be used by itself, but must be used together with the viewing distance in order to draw any conclusions about visual sharpness, and whether or not it qualifies as a retina display. While the iPhone 4 has an impressive 326 PPI, it is typically held relatively close and viewed from around 12 inches. Larger displays like tablets and laptops are typically viewed from 16 inches or more and need only 215 PPI to appear perfectly sharp with 20/20 Vision (what Apple calls a retina display ). In fact, existing 1920×1080 HDTVs, which are viewed from much larger distances, are already what Apple calls retina displays as explained in this display news article.
Read more at: Gizmodo