Olympus 1 has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized BSI-CMOS sensor and features TruePic VI processor. On the other hand, Olympus E-M5 II has a 16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features TruePic VII processor.
Below you can see the 1 and E-M5 II sensor size comparison.
As seen above, Olympus E-M5 II has a 5.4x Larger sensor area than Olympus 1. 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.