When Canon set out to make an ultra compact, ultra high resolution camera, it wasn't as simple as dropping a new CCD into an existing body. The reason for that is due to the size of the CCD sensor itself: on the SD200, SD300, and the new SD400, the CCD is 1/2.5" in size. But a 7.1 Megapixel sensor -- also used in the PowerShot G6 and S70 -- is physically larger (1/1.8"), so it wouldn't work in the SD200/300/400 body.



Link: DC Resource