PCI – (Peripheral Component Interconnect) – a bus used for connecting cards to the motherboard. The PCI bus can be used to connecting a network interface controller, sound card, internal modems, TV cards etc.
PCI-E – a system bus standard created as a replacement for older standards PCI, PCI-X and AGP. Used to connect any standard type of card (graphics, audio, network and others). Devices designed for PCI Express are not backwards compatible with any previous slot (AGP, PCI)