4. PCI, USB or FireWire?
In order to get the digital audio into the computer, the audio interface needs a suitable connection. Lets look at the various bus types or connections available to audio interfaces:
- PCI/PCI-X(Peripheral Component Interconnect)
A parallel data bus where multiple lines move the bits into the computer simultaneously (PCI 32 lines, PCI-X 64 lines). The PCI bus is part of the computer itself, and offers a connection directly to the motherboard in the form of a slot for a PCB (printed circuit board).
- FireWire/IEEE-1394(1394 is the designation of the Institute of Electrical and Electronics Engineers).
FireWire/IEEE-1394 is the best example of a serial bus. The data is sent one bit behind the other over a single pair of lines. This allows for the use of relatively long cable to be connected between the computers port and the external audio interface.
- USB(Universal Serial bus).
The other popular serial bus, favoured by Intel and Microsoft. While FireWire devices can communicate independently among themselves, USB uses a kind of tree structure hosted by the computer.
- CardBus/ExpressCard/PCMCIA(Personal Computer Memory Card International Association)
A laptop expansion slot which corresponds to a parallel PCI bus, only in a substantially more compact version and with the possibility of inserting the card from outside the computer.
- PCIe/PCI-E(PCI express, not to be confused with PCI-X)
Although similar to PCI in that its placed directly on the motherboard, they are fundamentally different in that PCIe is a serial bus. A single lane is about twice as fast as regular PCI, and PCIe can have up to 32 lanes moving up to 8GB of data per second.
Within the individual bus families there are variants with different speeds:
- FireWire 400 - up to 400 megabits per second (Mbit/s)
- FireWire 800 (1394b) up to 800Mbit/s
- USB 1.1 up to 12Mbit/s
- USB 2.0 - up to 480Mbit/s
- PCI (32bit/33Mhz) - 133MByte/s (1066Mbit/s)
- PCI-X (64bit/133MHz) - 1066MByte/s (8528Mbit/s)
- PCIe x1 (1 Lane) - 250MByte/s (2000Mbit/s)
- PCIe x16 (16 Lanes) - 4000MByte/s (32,000Mbit/s)
The graph should be viewed with some caution as it only represents theoretical maximums. In the real world, the speeds actually attainable can be much slower, but it is still helpful for a rough comparison.