Every scanner - no matter what manufacturer - has only one attached scan-resolution. This resolution is known either as optical resolution or physical resolution. The optical resolution is calculated easily by this formula:

For a VIDAR Atlas 600e e.g. this means:

This results in 562 dpi from which the overlapping area needs to be subtracted. According to that, the optical resolution of the VIDAR Atlas 600e is 508 dpi net.

"dpi" means "dots per inch"
1 inch = 1" = 25,4 mm

Beside the optical resolution our scanners can certainly produce data in any other resolution (between 50 dpi and the upper-limit for the certain scanner - see the overview table). This resolution is called interpolated resolution, since it is - starting from the optical resolution - artificially increased or decreased. Interpolation does not mean that the result is bad but at some extent the result will start to become dissatisfying.