Dpi means pixels per inch. Inches are on paper. Printers also use dpi. This dpi spacing establishes printed size. Dpi means pixels per inch.
Inches are on paper.
But show those 600 pixels on the screen , where there is no paper, and where inches have no meaning, and you simply see 600 pixels. One image pixel per screen pixel memory location, every time, regardless of the size of the screen. If you have a 640x480 pixel screen, you will see 600 pixels, nearly full screen size. If you have a 1600x1200 pixel screen, you will see 600 pixels, and it will fill much less of the screen area. But dpi has no effect at all on the screen.