PPI, or pages per inch,is a "thickness rating." A paper that is 400 PPI takes 400 pages to equal 1 inch.
DPI,Dots per Inch.The measurement of resolution for page printers, photo type setting machines and graphics screens. Graphics screens usually reproduce 60 to 72 dpi, most page printers 300 dpi, and typesetting systems 1,000 dpi.
