What are PCIe Lanes and Why Do They Matter?

What are PCIe Lanes

In our last post, we discussed the PCIe bus and the upcoming PCIe 4.0 but we only briefly touched on PCIe lanes themselves. So what are PCIe lanes and why do they matter? Read on to learn more.

What are PCIe lanes?

Without getting super geeky here, PCIe lanes are essentially how the PCIe devices communicate to the system through that PCIe bus. Similar to how multi lane highways work – with higher traffic areas needing more lanes to handle the volume – certain components require higher throughput, so require more lanes. You may see lane sizes referred to in terms of width but most commonly you’ll see “by” as in PCIe “by 8” or “x8.” Both of these denote eight PCIe lanes.

How many PCIe lanes do I need?

Each PCIe device requires a certain number of lanes to operate at full capacity.  Devices like graphics cards typically require x16 while slower devices like USB cards are fine at x1. Generally speaking, you want to make sure you have enough PCIe lanes to properly handle the TOTAL PCIe requirements for the devices you’ve chosen, so the answer to this question depends on your specific PC build. A brief list of common PCIe devices and the number of lanes they require are below for reference, but it’s good practice to verify these numbers with your specific components. Pick your devices, then total up the number of lanes required.

Component Lanes
NVIDIA Graphics 16
AMD Graphics 16
PCIe Storage (Intel 905p, Samsung 970 Pro, etc) 4
RAID cards 4 to 8
USB cards 1
802.11 Wifi 1

How many PCIe lanes with common processors

The number of available PCIe slots and types depends on the motherboard, but the total number of available lanes depends on the processor and chipset itself. Here is a list of common processors and the number of lanes each offers. When configuring a build, make sure you’re choosing a processor with enough PCIe lanes for your chosen devices.

Intel AMD
Processor PCIe Lanes Processor PCIe Lanes
Intel Core i5 8600k 16 AMD Ryzen 7 2600X 20
Intel Core i7 8700 16 AMD Ryzen 7 2700X 20
Intel Core i7 8700k 16 AMD Ryzen 7 2700 20
Intel Core i5 9600k 16 AMD Ryzen 7 2600 20
Intel Core i7 9700k 16 AMD Threadripper 1900X 64
Intel Core i9 9900k 16 AMD Threadripper 1920X 64
Intel Core i7 9800X 44 AMD Threadripper 1950X 64
Intel Core i9 9900X 44 AMD Threadripper 2920X 64
Intel Core i9 9920X 44 AMD Threadripper 2950X 64
Intel Core i9 9940X 44 AMD Threadripper 2970X 64
Intel Core i9 9960X 44 AMD Threadripper 2990WX 64
Intel Core i9 9800X 44

What if I run out of PCIe Lanes?

So you’ve done your homework, totaled up the number of lanes you need but either your motherboard doesn’t have enough slots or processor doesn’t have enough lanes. Well, to return to our highway analogy, what happens when too many cars use too few lanes? Same thing here. But that doesn’t mean your system is destined for a traffic jam. Most graphics cards run optimally with 16 lanes, but they will run with 8 if needed, though obviously not as well as when running at x16. This downclock happens in the background when more lanes are needed than are available without having to take any action to initiate, so aside from the performance hit, you’d likely not even realize it happened. After all, running a graphics card at x8 is not an ideal situation if you’re trying to maximize performance, but may be better than having to upgrade your processor.

Concerned your Velocity Micro build does not have enough lanes? Our team is here to help.

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Josh Covington

Josh has been with Velocity Micro since 2007 in various Marketing, PR, and Sales related roles. As the Director of Sales & Marketing, he is responsible for all Direct and Retail sales as well as Marketing activities. He enjoys Seinfeld reruns, the Atlanta Braves, and Beatles songs written by John, Paul, or George. Sorry, Ringo.

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