A image sensor It is an electrical device that converts light into an electronic signal which is then interpreted by an image processor that resulted in that file in JPEG or RAW that you manage.
The first digital camera many remember it was developed by Kodak, but the name of its inventor is Steven Sasson. Sensors in their day were CCD, CMOS, formerly a size then now are another. They have changed. We now have mobile phones, compact, CSC, reflex, medium format, … etc; in definitva lots of variety.
This small online tool, allows you to quickly clear all your doubts when it comes to knowing the sensor size of each camera in question as well as all the features of the sensor. Useful to know and compare several sensors one another.
Because also precisely you can see and compare easily features of the sensor of a compact, a CSC or a digital SLR.