Camera sensors have a base sensitivity that will capture an image without additional voltage applied to it. Adding voltage allows the sensor to capture more information, at the cost of additional noise. The lower ISO values are
also not usually the native, instead they are simulated in camera. The camera algorithms are pretty good these days, but they can still end up with clipping sensor data that you might want.
The native ISO isn't usually published along with typical product specs, but you can usually find it by searching online.