The Pci Express Overview

Peripheral Component Interconnect (PCI) is a computer bus designed for attaching hardware devices within a computer. The PCI interface is common in today's computers, and largely considered to be a ubiquitous internal PC connection. PCI-SIG, the industry organization chartered to develop and manage the PCI standard, released the PCI 1.0 specification in 1992. It was a component-level specification. The next year, the PCI 2.0 specification was released and was the first to establish standards for the connector and motherboard slot. PCI 3.0 is the most recent iteration of the standard; however, it is still under development within the PCI-SIG.

PCI Express
PCI Express (PCIe) is the latest I/O interconnect technology standard for PC expansion cards, and it was designed to ultimately replace conventional PCI standards. PCIe is used in consumer and industrial applications, including linking motherboard-mounted peripherals such as SATA drives, USB ports and sound cards and also as an expansion card for add-in boards.

PCIe uses point-to-point serial links, while earlier versions of the PCI standard use a parallel bus architecture. This makes bidirectional data transfer possible, enhancing performance when several device pairs are communicating simultaneously. PCIe remains compatible with legacy PCI solutions – a PCIe device can be used with older hardware based on earlier PCI specifications.

PCIe 1.0 and 2.0
PCIe technology is continuously developing and improving. In 2004, Intel first introduced the PCIe 1.0 specification. A version 1.1 soon followed, offering minor revisions to the specification.

In 2007, PCI-SIG announced availability of the PCIe 2.0 specification. This doubled the data rate of each lane and remained backward compatible with PCIe 1.1, so that last generation cards would still be able to work in machines with PCIe 2.0 slots.

ExpressCard
ExpressCard technology is a standard introduced in 2003. The ExpressCard standard delivers a thin, fast and light modular expansion to PC users. Consumers can add memory, wired and wireless communications cards and security devices to computers by inserting these cards into their systems. All ExpressCard slots accommodate modules designed to use PCIe or Hi-Speed USB (USB 2.0).

The ExpressCard slot has been included on mid- to high-range laptops including Apple's MacBook Pro line. Because laptops often only have one expansion slot, replacing the PC card slot with an ExpressCard slot results in a loss of compatibility with PC-card peripherals.

A PCIe card can fit into a slot of its size or larger. The number of lanes connected to a slot may be fewer than the number supported by the slot size. This allows for PCIe cards to be used without requiring the motherboard hardware to support the full transfer rate, which keeps down design and implementation costs.

PCI Express Benefits
Nearly all graphics cards released by ATI and NVIDIA use PCIe for connectivity to the PC's motherboard. NVIDIA leverages the high bandwidth data transfer capabilities of PCIe for its multi-GPU technology, which allows several graphics cards of the same chipset and model to run simultaneously, improving performance. ATI has also developed a multi-GPU system based on PCIe.

One theoretical application for External PCIe is giving a laptop computer the graphics capabilities of a desktop computer, by connecting the laptop to an External PCIe desktop video card. However, market development of external graphics solutions has been slow, and the use-case remains largely theoretical.

PCIe is often used for disk array controllers, onboard Ethernet and Wi-Fi, though add-in cards are typically conventional PCI. Because sound cards, modems, serial port cards and other cards with low-speed interfaces still use PCI, most motherboards supporting PCIe also offer conventional PCI slots.

PCIe 3.0
The next advancement in the widespread PCIe standard is PCIe 3.0. The future standard will offer double the bandwidth of PCIe 2.0, enabling higher data transfer speeds between the motherboard and devices. PCIe 3.0 is currently in development by the PCI-SIG and is anticipated to be released in Q2 2010. The PCI 3.0 specification will go through rigorous technical examination and evaluation before it is released to the industry. PCIe 3.0 offers backward compatibility with previous generations of PCI technology.

PCI Express Standards Testing
PCIe standards testing is used to test PCIe systems and add-in cards. Five PCIe compliance testing areas include:

Electrical testing: examines platform and add-in card signal quality
Configuration testing: examines configuration space of devices on add-in cards and checks for specification compliance
Link protocol testing: tests add-in Card compliance for Link protocol spec requirements
Transaction protocol testing: tests add-in Card compliance for Link Transaction protocol spec requirements
Platform BIOS testing: tests platform BIOS ability to recognize and configure devices

Another related test is PCIe compatibility testing, where several PCIe cards and systems are prepared to test whether PCIe devices are compatible with other products.

For PCIe 3.0 systems, add-in cards or devices to be placed on the Integrators List, the system or product must pass interoperability and compliance testing, and the vendor must submit a Product Listing Request Form for the tested device or system. The PCI-SIG Compliance Program is consistently rated the most significant benefit of PCI-SIG membership.

Working with a third-party testing facility will ensure that the product or system can comply with PCI compliance testing. For more information about PCIe standards testing, visit the PCI-SIG web site.

~Ben Anton, 2009

By: Ben Anton

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Ben Anton is a frequent writer for Allion Test Labs. SATA and PCI Express standards testing are just part of the device test services offered by Allion. Contact our experts to learn more about our PCI test tools and other services.