111-00481 X1132A-R6 NetApp 4-Port FCP Target 8Gb HBA PCIe card

 LSI Logic

For more than a decade the PCI bus has been the backbone of personal computers. Other systems, such as telephony and networking, adopted the technology for its cost and performance advantages. But now the PCI bus is reaching its performance limits. No longer able to scale in either clock frequency or bus width, PCI bus has no more bandwidth gains to make. It is time for a replacement.

Personal computer (PC) clock speeds have pushed to multiple GigaHertz. Networking and telephony applications are merging and demanding system throughputs in the hundreds of Megabytes per second. Meanwhile, the PCI bus that connects processors and their I/O resources is dragging along at a mere 133MHz. Something must change, yet the large installed base of hardware and software for PCI bus-based systems prevents designers from simply switching to a faster bus architecture. Systems need more bandwidth, but it must come with backward compatibility.

The PCI Special Interest Group (PCI SIG) has solved this dilemma with a new bus that offers higher throughput and frequency scalability while retaining software compatibility. The new bus, PCI-Express (PCIe), uses serial communications with a switched point- to-point connection at the hardware level. From a software standpoint, however, PCIe looks the same as traditional PCI to applications, drivers, and operating systems.

The need for a new bus comes from the inherent limitations of the traditional PCI bus. The bus was originally designed for use on a PC motherboard to connect add-in cards to the processor. A supplement to, and eventual replacement for, the original ISA bus, PCI provided a comparatively high bandwidth connection to peripherals. Like its predecessor, PCI bus matched the word size of the PC’s CPU, starting at a 32-bit width then moving to 64-bits. As processor clock speeds increased, so did the PCI bus speed. Starting with a 33MHz system clock, it moved through 66MHz and 100MHz to its present 133MHz speed.

Meanwhile, PCI bus found a home in other applications. The PCI bus serves as the backbone of network routers. Even though the routers do not follow the PC architecture, they use the PCI bus to take advantage of low-cost Ethernet-to-PCI adapters first developed for the PC. Similarly, PCI bus to Fibre Channel adapters have given rise to the storage area network (SAN), which uses PCI bus as its backbone.

x1132a-r6