PCI Audio Interfaces
PCI devices are "plugged-in" to your computer so you can expand its use (with more powerful soundcards for example).
The PCI bus is common in most modern PC's and also found on newer Mac's too.
It is a 64-bit bus though usually actually implemented at 32-bit
PCI interfaces come as an expansion card that slots into an available socket inside your computer, but sometimes they can also come as an integrated circuit board which fits onto the motherboard itself.
Considerations
A new standard - PCI Express (PCIe) - is already being adopted in the latest computers. Using PCI devices in the newer PCIe bus is said to be transparent, with no software changes necessary. There's more detailed info on PCIe at Wikipedia.
Computer Music sections
From M-Audio

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There are 7 reviews inside from other users.
From RME

The Multiface doesn't have the word 'multi' just because of the many different supported interface formats... No, it's because it's actually also multi-channel too!
The M... read more
Reviews: Yes!
Someone has an oppinion on the RME Multiface Hammerfall DSP 24/96K Interface inside. Might be worth reading if you're thinking of buying it.
From RME

Reviews: Yes!
Someone has an oppinion on the RME HDSP 9652 Hammerfall DSP 24/96K Digital PCI Card inside. Might be worth reading if you're thinking of buying it.
