[lemmings19]

High DPI refers to a high pixel density. High resolution refers many pixels.

If I have one million pixels on a 10cm by 10cm screen, and one million pixels on a 100cm by 100cm screen, they both have the same resolution because they both have the same number of pixels.

However, the 10cm screen has a much higher pixel density because the pixels are much smaller and closer together in order to fit on such a small surface.

The effect of a high pixel density is that you cannot tell pixels apart because they are so small and clustered, even up close. This results in a much more fine looking image.

'Retina' is just a marketing term for high DPI displays.

[adrianratnapala]

> High resolution refers many pixels.

That's correct, but only within our narrow jargon.

In optics, when I say "resolution", I mean the smallest distance (either angular or linear) beween two points that can be distinguished by the apperatus. E.g. "The CCD resolution is 10 microns per pixel". Not how many distinct points there are ("The CCD has 1024x786 pixels").

Sometime in the computer age, "resolution" became used for the latter meaning and so DPI had to be used where "resolution" was previously meant.

But don't blame people if they still use the original meaning.