What isn USB good for?
USB isn’t a replacement for every connector on your old PC. It’s maximum speed of 12 Mbps isn’t fast enough for high speed networking, digital video, fast disks, and other high performance peripherals. Other solutions such as SCSI or Firewire/iLink can fill these needs. Also, many older peripherals do not have USB built in. For these, there are a variety of USB adapters available.