ISO mode on DSLRs

[PhotoMoose]

This might be a silly question but how does the typical DSLR sensor implement different ISO speeds? Does the sensor actually somehow change sensitivity or is it a simple matter of multiplying the sensor's recorded input values by the ratio of the current ISO speed to the base ISO speed (e.g. 4x when using 4'' on a camera that supports 1'' at its slowest)?

 

[Brad Snyder]

Eric, start with the Wikipedia article here:

http://en.wikipedia.org/wiki/Film_speed

and then Google "Digital ISO".

There's some very technical stuff, some out of date stuff, some simplistic stuff. Fundamentally, I believe the answer is yes, increasing Digital ISO is an electronic/mathematical manipulation of the photon count the sensor saw.