An article on PCI Express

BY   HARISH. K

Brindavan College of Engineering Bangalore

Department of Electronics & Communication Engg

    PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed serial computer expansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards. PCIe has numerous improvements over the aforementioned bus standards, including higher maximum system bus throughput, lower I/O pin count and smaller physical footprint, better performance-scaling for bus devices, a more detailed error detection and reporting mechanism (Advanced Error Reporting, and native hot-plug functionality. More recent revisions of the PCIe standard support hardware I/O virtualization.

   The PCIe electrical interface is also used in a variety of other standards, most notably Express Card, a laptop expansion card interface. A lane is composed of two differential signaling pairs: one pair for receiving data, the other for transmitting. Thus, each lane is composed of four wires or signal traces. Conceptually, each lane is used as a full-duplex byte stream, transporting data packets in eight-bit 'byte' format, between endpoints of a link, in both directions simultaneously. Physical PCIe slots may contain from one to thirty-two lanes, in powers of two (1, 2, 4, 8, 16 and 32). Lane counts are written with an × prefix (e.g., ×16 represents a sixteen-lane card or slot), with ×16 being the largest size in common use. PCI Express operates in consumer, server, and industrial applications, as a motherboard-level interconnect (to link motherboard-mounted peripherals), a passive back plane interconnect and as an expansion card interface for add-in boards. In virtually all modern (as of 2012) PCs, from consumer laptops and desktops to enterprise data servers, the PCIe bus serves as the primary motherboard-level interconnect, connecting the host system-processor with both integrated-peripherals (surface-mounted ICs) and add-on peripherals (expansion cards). In most of these systems, the PCIe bus co-exists with one or more legacy PCI buses, for backward compatibility with the large body of legacy PCI peripherals.