Both Olympus 8000 and Casio EX-100 have 12.0 MP resolution sensors but Olympus 8000's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Casio EX-100's sensor is 1/1.7-inch (7.44 x 5.58 mm ).
Since Casio EX-100's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus 8000.
Below you can see the 8000 and EX-100 sensor size comparison.
As seen above, Casio EX-100 has a 1.5x Larger sensor area than Olympus 8000. 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.