Read this: Digital cameras have far surpassed film in terms of sensitivity to light, with ISO equivalent speeds of up to 409,600, a number that is unfathomable in the realm of conventional film photography. Faster processors, as well as advances in software noise reduction techniques allow this type of processing to be executed the moment the photo is captured, allowing photographers to store images that have a higher level of refinement and would have been prohibitively time consuming to process with earlier generations of digital camera hardware.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What is responsible for these vast increases in speed?
Faster processors, as well as advances in software noise reduction techniques