Two PCI slots supporting sixteen lanes each
Two PCI slots supporting sixteen lanes each
I appreciate the increased number of M.2 slots on modern motherboards, but they have their limits. When storage prices dropped, I questioned why more boards didn’t offer dual full 16-lane PCIe cards that support four M.2 drives. I once tried a card that fit but had to reduce its PCI lanes from 4 to 8 if the second slot was used. On the GPU side, a 3080 couldn’t handle the full 16 lanes because of PCI Gen 3 restrictions. I avoided buying it because only two of the four M.2 slots could power drives, so I added a budget single PCI x4 card and a cheap Gen 3 2TB M.2 for backups.
Could there be technical challenges preventing me from running multiple M.2 SSDs via a PCI card? Or is this a design choice to protect the HEDT market, where many boards came with a pre-installed PCI card for four M.2 slots—something seen by brands like Gigabyte and Asus before?
The limitation comes from the CPU's support for PCIe lanes. For instance, the AM4 socket provides 24 lanes, but only 16 are allocated for a video card, with additional lanes for the chipset and M.2 slot. The remaining lanes come from the chipset itself. With newer standards like PCIe 4.0 and PCIe 5.0, maintaining signal quality becomes increasingly difficult due to shorter trace distances. This necessitates spacing between PCIe slots to accommodate larger cards, along with buffers or amplifiers to preserve signal integrity—chips for this purpose are costly.
Thanks for the details... It's quite a challenge with a full custom waterloop and a straightforward PCI card holding a 4.2-inch drive. A simple swap of the SSD would be a huge help—no major modifications needed. I hope upcoming designs will address these current limitations.
The boards and CPUs are available, but mainly reserved for workstation systems. For instance, Threadripper offers many PCIe lanes. Mainstream platforms often lack extensive PCIe connectivity to cut costs, since most users have just one GPU plus a few NVMe drives—extra slots aren’t necessary. They also limit this to avoid hurting sales of their workstation or HEDT products. Those requiring significant PCIe capacity usually use the system for business applications and are prepared to invest more for the required features.
It's improbable this will occur, as bandwidth improvements with PCIe 5.0 could justify keeping or lowering the number of lanes on consumer devices.
This was what I considered but I thought they might gradually move into the more consumer-focused market. That sounds like hopeful thinking. I was expecting the shift from HDDs to SSDs and the compact M.2 design to encourage the development of PCI card options. It’s interesting to note that now I can purchase four 2TB M.2 drives for less than $400, whereas my initial purchase of a 2GB HDD cost over $700. That made me dream about assembling a card with four 4TB drives later on. Well, that’s enough. Thanks again for the insights.
more lanes on desktop won't materialize. Focusing on the motherboard market shows that converting those lanes into numerous slots is now uncommon. Each board typically has just one X16 slot in the second position, plus a couple of 1x slots, with the remainder being M.2 and plastic heat sinks. In contrast, I've got AMD EPYC set up right next to my desk.