-Optical Resolutions, this is the one that seems to matter the most. The optical resolution relates to the CCD's as discussed earlier. The higher the better. This is how many CCD's are on the scan head. But the optical resolution isn't the only thing to worry about. We have to worry about mechanical resolution.
-Mechanical Resolution, The number of steps the scan head makes per inch while scanning is the mechanical resolution. This amount to a 300dpi mechanical resolution stops every 1/300th of an inch or a 600dpi will stop every 1/600th of an inch. The more the better again. This can increase detail of the image or document. Take note that this is only taking a snapshot of your image or document vertically not horizontal. The horizontal is always done by Optical Resolution. The biggest factor that comes into play is how accurate is the scanners motor? If you bought a really cheap scanner this is a good question. Not only do you have to worry about the Mechanical and Optical Resolutions but we also have what's called Interpolation Resolution.
-Interpolation Resolution, this is a funny one. To break it down it is more software than anything. This resolution tries to guess what is between the CCD snapshots. In a nutshell filling in what it missed. When you take a small graphic and blow it up you don't want a bunch of blanks spots or to blocky, this is were interpolation comes in.
Scanners - Resolutions You Need 
