Olympus E-500 has a
8.0MP Four Thirds (17.3 x 13 mm ) sized CCD sensor . On the other hand, Sony A100 has a
10.0MP APS-C (23.6 x 15.8 mm ) sized CCD sensor .
Below you can see the E-500 and A100 sensor size comparison.
As seen above, Sony A100 has a 1.7x Larger sensor area than Olympus E-500. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.