Understanding PCI Bus, PCI-Express and In finiBand Architecture

There is some confusion in the market place concerning the replacement of the PCI Bus (Peripheral Components Interface) by either the InfiniBandSM Architecture (IBA), PCI-Express (formerly 3GIO Third Generation I/O), or upgrades to the PCI bus itself. Initially the InfiniBand architecture was viewed as the replacement for the PCI bus, yet the PCISIG (PCI Special Interest Group) recently announced that PCI-Express would replace the PCI bus. To make matters more confusing the PCISIG also recently introduced a draft specification for PCIX 266 (also called PCI-X DDR Double Data Rate) as the next upgrade to the PCI bus. So which is correct? Actually none of these technologies “replace” the PCI bus but rather provide upgrade paths with different levels of backwards compatibility and new capabilities. It is important to make a distinction between these technologies to help clear the confusion. Much of this confusion stems from viewing InfiniBand as strictly a chip-to-chip or local bus connection such as PCI and PCI-Express. In reality InfiniBand is much more than a local bus and thus it does not make sense to compare PCI or PCI-Express to InfiniBand. This paper will discuss how these technologies interact and complement each other.