PCIe 3.0, PCIe 2.0 and PCIe 1.1 Interface Differences

With silicon for PCI Express® 3.0 on the horizon from chip vendors such as Intel®, PLX Technology®, IDT® and others, it might be a good idea to review the interface differences of PCI Express 3.0, PCIe 2.0 and PCIe 1.1. Understanding these interface differences will enable successful integration of the latest PCI Express interface technology into embedded computing applications.

Does it matter that the single board computer / system host board and option card interface is PCI Express version 1.1, 2.0 or even the upcoming PCIe 3.0? Not really, because the basic SBC to option card interconnect functionality is not affected by PCIe version. The reason for this is that the PCI-SIG (Peripheral Component Interconnect Special Interest Group) did a smart thing when PCI Express 1.1 was first developed. The PCI-SIG built the basic PCIe interconnects in such a manner as to ensure both scalability and backwards compatibility between differing PCIe interfaces.

This critical specification feature enables the computer’s SBC / SHB, embedded motherboard or backplane hardware to operate with just about any PCI Express option card regardless of interface version. The potential for increased data throughput and performance within an embedded computing system is the primary application difference between the PCI Express 3.0, 2.0 and 1.1 interfaces.

A PCI Express 2.0 COTS board installed in an industrial computer will send its data over to the system host board (SHB) twice as fast as older PCI Express 1.1 boards. Of course, this assumes that the systems’ SHB has PCIe 2.0 interfaces. The same scenario plays out in an embedded motherboard. If the motherboard is equipped with PCIe 2.0 card slots then any PCIe 2.0 card placed into one of these slots will send it’s data to the board’s CPUs twice as fast as in a PCIe 1.1 system. This speed advantage is cumulative and can be critical in high-performance computing applications.

Summary of the key parameters of the various PCI Express interfaces:

Base Clock Speed: PCIe 3.0 = 8.0GHz, PCIe 2.0= 5.0GHz, PCIe 1.1= 2.5GHz

Data Rate (per lane & per direction): PCIe 3.0 = 1000MB/s, PCIe 2.0= 500MB/s, PCIe 1.1= 250MB/s

Total Bandwidth (x16 link): PCIe 3.0 = 32GB/s, PCIe 2.0= 16GB/s, PCIe 1.1= 8GB/s

Data Transfer Rate: PCIe 3.0 = 8.0GT/s, PCIe 2.0= 5.0GT/s, PCIe 1.1= 2.5GT/s

PCIe 3.0 features a number of interface architecture improvements, but communicates at the same interface speeds used in PCIe 2.0. PCIe 3.0 achieves twice the communication speeds of PCIe 2.0 through various architecture and protocol management improvements. PCIe 3.0 silicon will start becoming readily available in 2011.

Single board computers such as the Trenton JXT6966 system host board and JXTS6966 support a wide variety of PCI Express option card interfaces. Products such as the Trenton NTM6900 or the WTM7026 embedded motherboard feature multiple PCI Express option card slots while the Trenton BPC7041 and BPC7009 backplanes are examples of PICMG 1.3 backplanes with built-in PCI Express 2.0 embedded computing hardware support.