I know the basic function of resistors and capacitors. I know filters, oscillators, one-shot, differentiator/integrator, ADC/DAC, power supplies, etc. But in a motherboard why are there so many external resistors and capacitors? How many of these analog circuits are there? Or does it have something to do with the copper transmission lines?
They provide filtering, DC smoothing, adjustment (voltage, current, frequency of an IC), pull-ups and pull-downs, impedance matching, terminations, current limiting, DC blocking, basically all the functions that are included as options for ICs, that can't be placed inside ICs or that can be done cheaper or occupy less space than an additional IC.