As many as 30 bits of data can be used to describe one pixel. This allows more than 16,000,000 variations of each color. This is the color depth . However, the memory necessary to store even a small image is enormous. These are the devices that connect to the computer and under the computer's control break up an image into pieces or pixels.
Most scanners are capable of higher resolutions.
Scans of 200 or 400 DPI are not unusual. Simply plug in 200 where 72 is above and you'll see the file size grow dramatically. Most display devices like monitors and color ink jet printers allow for re-sizing the image. The only time the DPI makes a difference is when an image of low DPI is expanded to an inappropriate size. For example, these images have identical DPI's and color depth.