Mate, Resolution being 800 X 600 implies that the screen has 480,000 pixel points that will be used to render the screen(This is often confused with the dimensions of the display). DPI or PPI means dots/points per inch, this is the measure of the density of the screen.
So just given the Resolution, one can not determine the actual length of the display unless the density parameter is also available. So a 800 X 600 resolution has 480,000 Pixel points & a let this device has a density of 480 dpi.
So the Width of the screen
= No of pixel points along its width/Density
= 800/480
= 1.67 inches
Similarly,
Height = 600/480 =1.25 inches
and if 800X600 resolution device has density of 160 dpi, its dimensions will vary drastically. Following calculations calculate Height/Width of 800X600 on 160 dpi. Compare these two values with above 480 dpi calculations.
the Width of the screen = No of pixel points along its width/Density
= 800/160
= 5.0 inches
Similarly,
Height = 600/160 =3.75 inches
This is the very reason that scaling images to best fit the screen is such a complex issue on frafmented android environment.However, I love android!
Hope this helps! and any one who has some thing to add/delete.modify to this answer is most welcome.