i don't understand a lot of this computer "stuff."
The ATMEGA328 specs say it can sample at 20MHz
PhotoDiode sensor with a max output of 17MHz and min of 12.5kHz depending on the setting
analogRead function can only process at 10,000 samples/sec
or will it just store the input sample data until it can convert the data
It takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.