Sony A580 has a 16.0MP APS-C
(23.5 x 15.6 mm ) sized CMOS sensor and features Bionz processor. On the other hand, Sony A100 has a 10.0MP APS-C
(23.6 x 15.8 mm ) sized CCD sensor .
Sony A580's sensor provides 6MP more than Sony A100's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the A580 and A100 sensor size comparison.
Sony A580 and Sony A100 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
DxOMark Sensor Scores
Both Sony A580 and Sony A100 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, A580 has scored 80, 19 points higher than A100.