How can this be right? A 960x640 resolution screen on a 10 inch screen would still be 960x640 resolution.
The DPI would be a lot lower, because the pixels would need to be bigger, to fill the greater screen size.
Surely resolution and DPI are different things?
You are correct. The resolution is horizontal*vertical pixels.
Where many have gone wrong (ahem, arn) is saying that resolution is along one dimension. It is not. It is measured in two dimensions (vertical x horizontal).
Pixel density is how many pixels per square inch, and can be anything. A 65 inch plasma has a resolution of 1920x1080. So does a 46 inch plamsa or LCD. So does a 21.5 inch cinema display. Etc. All the same resolution. Yet all have different pixel densities.
If the iPhone increases its screen size and keeps its 960x640 resolution, then the pixels will have to be a bit larger, and so the pixel density will be a bit lower.
Yet, oddly, when people were talking about the iPad getting a retina display of 2048x1536, it was referred to as a resolution "doubling". That is wrong. It's a quadrupling of the resolution. 4 times as much information is being displayed. 4 times as many pixels.
A *doubling* of the current iPad resolution would be roughly 1448x1086.
One more example: iPhone 4 has 4 times the resolution of iPhone 3, ie 960x640 is 4 times 480x320. 4 times the number of pixels. 4 times the resolution. Screen size is irrelevant.
One more time for the road: resolution is measured in 2 dimensions, not one. It is not dots per inch. It's vertical dots multiplied by horizontal dots.