The bandwidth of two cards in a RAID 0 array is about the same as one card alone. However, it's not because the adapter bus is too slow (It's up to 886x!), but because the adapter is based on an ATA interface which cannot interleave commands (like a SATA interface can), so it must initiate and complete a read from one card, then the other and back again. Some video cameras (for example, Red RAID) spreads the data across two cards, so It is necessary to insert both cards simultaneously for retrieval. Having two slots makes this possible.