A common "Trick" was to buy cards that had essentially their own processors to handle this stuff - SoundBlasters, 3Com nics, IDE drive controllers that had their own processor (hell, even up to their own OS) since that freed the CPU up for doing actual work - gaming. Even an external or other
CPUs were a bottle neck but most people didnt tax the single core machines doing most daily work (office work, browsing the web) so it was fine, but once you load up a game that needs sound, 3d, networking, disk access all at once it would start stealing clock cycles trying to do all of that in one place.