Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos.
Cameras with higher effective ISO will be better choices for indoor photography, night shooting, and indoor sports photography, especially if you intend to make large prints.
You can learn more at our glossary entry.
Maximum effective ISO test data courtesy of DxO Mark.EOS M100 test data on DxO Mark E-M10 test data on DxO Mark
Great image quality especially from RAW files; Excellent dynamic range for a Four Thirds sensor; Very good high ISO performance; Realistic colors and excellent hue accuracy; Built-in Wi-Fi with remote control and sharing features; Improved HD video; Lightweight and very portable; Built-in pop-up flash; Minimal EVF lag time.
Contrast-Detect AF struggles with small and low-contrast subjects; Mediocre battery life; No external microphone or headphone jack; Mediocre burst speed with continuous AF; No weather sealing; Heavy-handed high ISO noise reduction.