Ricoh GR Digital IV has a
10.0MP 1/1.7-inch (7.44 x 5.58 mm ) sized CCD sensor . On the other hand, Sony RX100 has a
20.0MP 1-inch (13.2 x 8.8 mm ) sized CMOS sensor .
Sony RX100's sensor provides 10MP more than Ricoh GR Digital IV'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 GR Digital IV and RX100 sensor size comparison.
As seen above, Sony RX100 has a 2.8x Larger sensor area than Ricoh GR Digital IV. 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.