Spectrum PCI Express Compatibility Chart

PCI Express Lane Chart

This chart shows the compatibility and the maximum transfer speeds for the different Spectrum products and PCI Express bus versions. Please note that the transfer speed shown here is a measured figure from a reference system. The reached transfer speed in your system is also depending on the motherboard, the operating system and other devices in the system and may be less.

Please note that PXIe always has 8 physical lanes. The resulting transfer speed depending on the electrical connection is shown in the next chapter.

Difference between physical and electrical lanes

The above chart shows the limitations for physical connections (size of the connector itself). Luckily a lot of motherboard manufacturers, especially server based manufacturers, tend to use larger physical connectors than lanes are electrical connected. This may lead to the fact that a Spectrum PCI Express x8 card is used inside a physical x8 connector which has only 2 or 4 lanes connected electrically.

This combination works fine for all Spectrum cards but limits the transfer speed to the speed the electrical connections can handle.

The following table shows the different transfer speeds one can achieve based on the electrical connection:

Payload size

All motherboards internally have a PCI Express payload size that heavily influences the maximum transfer speed that can be reached. The maximum payload size is normally depending on the chipset the manufacturer is using but can also be decreased by other devices that are connected to the chipset. While in theory the payload size can have a lot of different values, in real life (2014) all chipsets either have a payload size of 128 bytes or 256 bytes. The following performance was measured in a PCI Express x8 Gen 2 interface:

• 256 bytes payload size: read (acquisition) transfer speed of 3380 MB/s, write (replay) transfer speed of 2820 MB/s
• 128 bytes payload size: read (acquisition) transfer speed of 3000 MB/s, write (replay) transfer speed of 2000 MB/s

Lane configuration in the BIOS

On some motherboard the lane configuration of slots can be programmed in the BIOS. This configuration normally allows to either have one fast slot with full number of lanes or two mid speed slots with each half number of lanes using. In case that one slot is used with full speed the other slot is normally not usable then. Please check your BIOS settings and the motherboard manual when encountering non-expected transfer speed results.