PCIe expansion cards They are some of the most powerful, as well as affordable, upgrades you can make to a PC. The PCIe bus offers a high-bandwidth connection to the system, and the versatility of the various PCIe sockets is a boon for advanced users hoping to expand the capabilities of their equipment. If you have one or more PCIe cards installed on your motherboard, they may only be running at half their maximum speed. Due to motherboard design and PCIe lane sharing, your expansion card might run in x2 mode instead of x4 (or x4 instead of x8). Not all PCIe slots on the motherboard are connected with the same number of PCIe lanes, so choosing the wrong slot can easily speed up your PCIe card. It is possible to check if this is actually happening on your system and often swapping slots can fix the problem.
High bandwidth PCIe cards typically require 4 lanes
It’s not always easy to know if you’re really getting them all.
the lack of PCIe lanes available It’s not always a problem on modern motherboards. For example, low-bandwidth expansion cards, such as USB, Wi-Fi, SATA, and even 10GbE adapters, do not need anything more than a PCIe 4.0 x1 slot. A single PCIe 3.0 lane (or PCIe 4.0 for 10GbE NICs) is enough to supply them with all the bandwidth they can use. However, when it comes to NVMe adapters, HBA cardsor 4K capture cards, it is often necessary to run them at x4 or x8 configurations. Even if the PCIe slot you are using is physically an x16 slot, it may be wired with only 4 or 8 lanes, depending on your motherboard design.
The problem here is that the motherboard BIOS will often not show any indication that your PCIe card is running at a speed lower than its maximum rated speed. Your dual NVMe adapter may only have 4 lanes, while you need at least 8 to allow both SSDs to operate at their maximum bandwidth. Depending on the purpose of the PCIe card, you may not even notice a difference in perceived performance. However, you could be suffering from a real performance loss, especially in intensive workloads. Your file transfers could slow down or your 4K streaming could degrade or be plagued with stability issues.
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SAS 12Gb/s
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Your PCIe card running in x2 mode is not at all uncommon
It’s about the design of the PCIe lane
Most high-performance PCIe cards require a x4 configuration to operate at their maximum speed. However, for various reasons, they often run out of enough PCIe lanes and are forced to operate in x2 mode. This can happen if you install the card in the “wrong” slot. The PCIe slots on your motherboard have a varying number of PCIe lanes routed to them. Some slots, such as the main x16 slot, receive 16 lanes and are connected directly to the CPU, while others only have 1, 2, 4, or 8 lanes and could be connected to the chipset instead. Even if your motherboard has a full-size secondary and tertiary PCIe slot, chances are it won’t have 16 lanes available. Therefore, it is necessary to consult your motherboard manual before choosing which empty PCIe slot for use with your high bandwidth expansion card.
Another reason why your PCIe expansion card is running at reduced bandwidth could be PCIe lane sharing. Even if the physical slot you are using has enough lanes to fully support your PCIe card, other devices connected to certain M.2 or SATA ports may reduce the PCIe lanes available for the PCIe slot in question. Because all of these slots come from a shared PCIe pool, you must choose which slots to prioritize.
Check if your PCIe card is really running slower
The proof is in the pudding.
Checking if a SSD runs at half speed It can be done at CrystalDiskInfo and GPU-Z can confirm your suspicions in the case of a graphics card. However, for your PCIe expansion cards, you can use AIDA64. This tool is primarily known for its stress testing capabilities, but it can also show you the current and maximum link speed for all PCIe devices installed on your PC. You can compare the active speed with the maximum speed to see if your expansion card is really running at a reduced speed. Once you have confirmed the discrepancy, you will need to resolve it.
Fixing reduced bandwidth on your PCIe card is as simple as swapping out the PCIe slot for one that has more lanes available. Alternatively, you can remove certain SATA or M.2 devices or reposition them so that the PCIe slot your card is currently installed in receives enough lanes to run it at its maximum speed. You can verify the change in AIDA64. Motherboards with high-end chipsets enjoy a higher number of PCIe lanes, allowing enthusiasts worry relatively less about sharing PCIe lanes.
Don’t Unknowingly Block Your PCIe Expansion Cards
PCIe cards are some of the most powerful additions to any PC. They can add newer features to older PCs and expand the capabilities of newer machines. However, your motherboard’s PCIe lane design can sometimes force your PCIe cards to operate at reduced bandwidth. Due to shared use of PCIe lanes, not all PCIe slots enjoy the maximum number of lanes for which they are rated. Depending on the devices you have connected to the motherboard, some slots take priority over others. Knowing the difference between them allows you to run your PCIe cards at their maximum speeds.
