Be aware of PCIe lane limits
It’s not so plug and play.
It’s common wisdom that adding a fast NVMe SSD will greatly speed up the responsiveness of your system. That’s definitely the case, but what happens if you insert a second or third drive into your shiny motherboard? All too often, sadly, you have to delve into the depths of the motherboard manual to see if you’ll get what you think you’ll get. In some cases, a drive or some other system component may not function at all. It’s a real mess and I wish the manufacturers made it a little easier for non-expert users to understand. The obvious solution is of course, to add more PCIe lanes!
The problem lies with the CPU manufacturers and their platforms. The desktop Socket 1200 and AM4 CPUs are stuck with a limited number of PCIe lanes, even more so on the budget chipsets. 16 of these lanes are allocated to the primary PCIe slot. The rest are typically routed to a single M.2 slot or the chipset, which in turn has its own set of available lanes.
AMD leads with its PCIe support. Of course its chipsets are configured differently, but the X570 and B550 platforms both support PCIe 4.0, which double the bandwidth of the PCIe 3.0 lanes that Intel use. X570 notably features 24 PCIe 4.0 lanes from the CPU, which is usually allocated with 16 to the primary PCIe slot, four to an NVMe slot and four to the chipset. From the chipset, an additional eight lanes can be used for additional slots or controllers. AMD has it mostly right. A typical system configuration is able to run without compromise.
Intel hasn’t caught up (officially at least, but PCIe 4.0 on Z490 is a story for another day). It lags behind with ageing PCIe 3.0 support and a relatively slow DMI 3.0 CPU to chipset link. While you can run several NVMe drives, the DMI link can be a bottleneck. Both AMD and Intel desktop platforms can also force disable other components of you run several NVMe or SATA M.2 drives. Usually SATA ports or a PCIe slot is disabled. We deserve better in 2020.
Both Intel and AMD use additional PCIe lanes as a selling point for their high end desktop platforms. If you move up to the HEDT platforms, PCIe lanes are not an issue. The Threadripper TRX40 platform supports up to 72 PCIe 4.0 lanes. That’s the bandwidth equivalent of 144 PCIe 3.0 lanes! With that kind of capacity, you can run as many GPUs, SSDs, expansion cards and peripherals as you want. Intel’s X299 platform is also well equipped with up to 68 lanes, although they are the slower PCIe 3.0 variety.
If Intel and AMD (and the motherboard manufacturers by extension) want us to pay $500+ for a mainstream motherboard, give us something to justify it! More PCIe lanes please. Let us run two or three M.2 drives at full speed without disabling SATA ports or a PCIe slot. So what if the CPUs need more pins or the socket is larger. If you want us to pay more, give us more!
“The problem lies with the CPU manufacturers and their platforms. The desktop Socket 1200 and AM4 CPUs are stuck with a limited number of PCIe lanes, even more so on the budget chipsets.”