About the times _before_ USB (Universal Serial Bus): On the Apple side of things, we used ADB (Apple Desktop Bus) for things like keyboards and mice (replaced by USB), RS-422 (a serial bus) for printers etc. (replaced by USB) and SCSI for scanners, ext. harddrives etc. (replaced by FireWire)... It was actually even more complicated than that. Once you start counting the various options for LocalTalk, EtherTalk etc. as well as the special monitor cabling the Macs used... Apple had to clean things up, and with adopting USB and creating FireWire - and pushing those technologies almost without a way back (there were USB-2-ADB adapters and things like that from 3rd party vendors and there was an "almost-supported" ADB port on the first Blue&White G3 PowerMacs) - they did the right thing. And early so, if you look at the overall PC market. We shouldn't forget that Sony did their part in spreading FireWire (their iLink) technology among consumers, too. And once Apple had created a market for USB-devices, PCs adopted the new standard quite quickly, too.
Apple, of course, was _very_ late to adopt USB 2.0, because they wanted FireWire to take off. (They only adopted USB 2.0 when FireWire 800 was ready.)