Answered: Can I Put a PCIe x4 or x8 Card in an x16 Slot?

Learn whether you can insert an x4 or x8 PCI-Express card in an x16 slot or any other size combination.

PCI-Express Kevin Jones / TechReviewer

Last Updated: September 10, 2021

Written by Kevin Jones

Can I Use an x4 or x8 Card in an x16 PCIe Slot?

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You can use PCIe cards of a lower lane width (e.g., x2, x4, or x8) in a higher lane width slot (e.g., x16).

PCI-Express will negotiate how many lanes will be used, and your card will work at its full speed, assuming the PCIe slot has the same or higher PCIe version.

To be thorough, these non-matching PCIe card and slot sizes all work:

  • x1 PCIe card in an x2 PCIe slot
  • x1 PCIe card in an x4 PCIe slot
  • x1 PCIe card in an x8 PCIe slot
  • x1 PCIe card in an x16 PCIe slot
  • x2 PCIe card in an x4 PCIe slot
  • x2 PCIe card in an x8 PCIe slot
  • x2 PCIe card in an x16 PCIe slot
  • x4 PCIe card in an x8 PCIe slot
  • x4 PCIe card in an x16 PCIe slot
  • x8 PCIe card in an x16 PCIe slot

Don't forget to check out my Recommended PCIe 4.0 CPUs and Motherboards (TR) below.

What Are PCIe Lanes?

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PCIe lanes are connections between a PCI-Express (TR) expansion card or device and the CPU. PCIe lanes often communicate with the CPU via chipsets on the motherboard. Each PCIe lane is composed of 4 wires (two differential pairs).

With naming similar to a road, the number of lanes is referred to as the lane size, or how many lanes wide a link or port uses. A single lane is referred to as x1 or "one lane wide."

The maximum throughput (speed) is multiplied by the number of lanes. An x8 PCIe port has twice the throughput of an x4 port.

Some CPUs and motherboards provide PCI-Express lanes at multiple PCIe versions. In these cases, you can choose which devices need the most bandwidth to decide which should be connected to the highest version PCIe lanes. While laying out your system, keep in mind that PCIe speeds will be based on the lowest PCIe version between the slot/port and the device.

You can insert a PCIe add-in card (AIC) into a slot that supports a higher number of lanes. In this case, it would use up to the number of PCIe lanes that the card has. For example, you could insert an x4 PCIe network card into an x16 PCIe AIC slot, and it would run at full x4 speed.

In various scenarios, a PCIe device may not use the maximum number of lanes for which the device was designed. For example, some motherboards have x8 PCIe ports that are only electrically wired for x4 lanes. In another case, a system may have limited lanes provided by the CPU, distributed based on availability or configuration.

Devices will negotiate the number of lanes to use, based on system availability, and should still perform fine at a reduced overall bandwidth in most cases. Refer to your motherboard's documentation and CPU specifications to determine PCIe lane quantities and allocations.

Do I Need an Adapter to Put a Shorter PCIe Card in a Longer Slot?

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No adapter is needed for inserting a shorter PCIe card into a larger PCIe slot. PCI-Express will negotiate how many lanes will be used, and your card will work at its full speed, assuming the PCIe slot has the same or higher PCIe version.

Are PCIe Versions Backward Compatible?

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PCI-Express (TR) versions are backward compatible, meaning that you can use a PCIe 4.0 graphics card or storage device on a PCIe 3.0 or PCIe 2.0 system. However, PCI-Express will use speeds based on the lowest of the two versions for communication. For example, if you use a PCIe 3.0 NVMe SSD with a PCIe 4.0 system, the SSD would be running at PCIe 3.0 speeds.

Reducing the PCIe version would halve the max potential bandwidth. However, you may not experience a performance impact if your device is not using the available bandwidth.

You can refer to the following table to determine the bandwidth limit and decide whether that is adequate for your needs.

PCI-Express Speeds (Rounded)
x1 Bandwidthx2 Bandwidthx4 Bandwidthx8 Bandwidthx16 Bandwidth
PCIe 1.0 250 MB/s 500 MB/s 750 MB/s 2 GB/s 4 GB/s
PCIe 2.0 500 MB/s 1000 MB/s 2 GB/s 4 GB/s 8 GB/s
PCIe 3.0 1 GB/s 2 GB/s 4 GB/s 8 GB/s 16 GB/s
PCIe 4.0 2 GB/s 4 GB/s 8 GB/s 16 GB/s 32 GB/s
PCIe 5.0 4 GB/s 8 GB/s 16 GB/s 32 GB/s 63 GB/s
PCIe 6.0 8 GB/s 16 GB/s 32 GB/s 63 GB/s 126 GB/s

Learn more about PCIe's backward compatibility in Is PCIe Backward Compatible? (TR).

Our Favorite PCIe 4.0 CPUs and Motherboards

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Best AMD High-Frequency CPU: AMD Ryzen 9 5900X

  • Up to 4.8 GHz: perfect for games, video editing, and high-intensity tasks.

  • 12 cores / 24 threads: High core count for the frequency! This combination makes it a great all-around system that can handle almost any job.

  • Check the latest price of the AMD Ryzen 9 5900X on Amazon (affiliate link).

    AMD Ryzen 9 5900X AMD Ryzen 9 5900X Check Price on Amazon (affiliate link)
  • For the AMD Ryzen 9 5900X CPU, you'll need a 5000 series motherboard with the X570 chipset to support PCIe 4.0.

  • Our recommended motherboard to pair with the Ryzen 9 5900X is MSI's MAG X570 TOMAHAWK WIFI Motherboard: MSI MAG X570 TOMAHAWK WIFI MSI MAG X570 TOMAHAWK WIFI Check Price on Amazon (affiliate link)

    • PCIe 4.0 support
    • One 2.5 Gb Ethernet port is faster than most Internet speeds, with room to spare for file transfers.
    • Two NVMe M.2 (TR) slots both run at PCIe 4.0 speeds.
    • Wi-Fi 6 provides great Wi-Fi speeds (not Wi-Fi 6E, but still really good).
    • USB 3.2 Gen 2 offers 10 Gbps USB speeds.
    • Check the latest price of the MSI MAG X570 TOMAHAWK WIFI Motherboard on Amazon (affiliate link).

Best Intel High-Frequency CPU: Intel Core i9-11900K

  • Up to 5.3 GHz: perfect for games, video editing, and high-intensity tasks.

  • 8 cores / 16 threads: Quite a few cores considering the frequency! This combination makes it a great all-around system that can handle almost any task.

  • You'll want to use a good cooler, as the "Thermal Velocity Boost Frequency" feature will improve your clock speed based on how cool you can keep it.

  • Virtualization features make it great for running virtual machines.

  • Check the latest price of the Intel Core i9-11900K on Amazon (affiliate link).

    Intel Core i9-11900K Intel Core i9-11900K Check Price on Amazon (affiliate link)
  • For the Intel Core i9-11900K CPU, you'll need a motherboard with the Z590 chipset to support PCIe 4.0.

  • Our recommended motherboard to pair with the i9-11900K is ASUS's ROG Maximus XIII Hero: ASUS ROG Maximus XIII Hero ASUS ROG Maximus XIII Hero Check Price on Amazon (affiliate link)

    • PCIe 4.0 support
    • Wi-Fi 6E makes it easy to reach the fastest speeds and future-proof your Wi-Fi system.
    • Four NVMe M.2 (TR) slots, which is a lot! (Only two of them run at PCIe 4.0 speeds)
    • Two 2.5 Gb Ethernet ports are faster than most Internet speeds with room to spare for file transfers.
    • USB 3.2 Gen 2x2 offers 20 Gbps USB speeds!
    • Check the latest price of the ASUS ROG Maximus XIII Hero on Amazon (affiliate link).

Best High-Core CPU: AMD Ryzen Threadripper 3990X

  • 64 cores / 128 threads: Insane number of cores/threads.

  • This CPU is going to be best for high-intensity multi-threading such as:

    • 3D graphics rendering (e.g., Blender/3DS Max/Maya)
    • CAD design, simulation, and visualization (e.g., AutoDesk Inventor)
    • Software that does a lot of physics analysis
  • Due to the high price, this CPU is best for business use-cases.

  • Check the latest price of the AMD Ryzen Threadripper 3990X on Amazon (affiliate link).

  • AMD Ryzen Threadripper 3960X (affiliate link) is a backup option if this one isn't in stock and for lower budgets.

    AMD Ryzen Threadripper 3990X AMD Ryzen Threadripper 3990X Check Price on Amazon (affiliate link)
  • For the AMD Ryzen Threadripper 3990X CPU, you'll need a motherboard with the TRX40 chipset to support PCIe 4.0.

  • Our recommended motherboard to pair with the AMD Ryzen Threadripper 3990X is ASUS's ROG Zenith II Extreme Alpha: ASUS ROG Zenith II Extreme Alpha ASUS ROG Zenith II Extreme Alpha Check Price on Amazon (affiliate link)

    • PCIe 4.0 support
    • Five NVMe M.2 (TR) slots all run at PCIe 4.0 seeds, which is insane!
    • One 10 Gb Ethernet port would allow you to transfer a 1 GB video file in under a second!
    • 1 USB 3.2 Gen 2x2 offers 20 Gbps USBs speeds; 9 USB 3.2 Gen 2 ports provide 10 Gbps; 8 USB 3.2 Gen 1 ports provide 5 Gbps; 3 USB 2.0 ports
    • Wi-Fi 6 provides great Wi-Fi speed (not Wi-Fi 6E, but still really good).
    • Bluetooth 5.0 (TR) is great for streaming music to Bluetooth headphones.
    • Check the latest price of the ASUS ROG Zenith II Extreme Alpha on Amazon (affiliate link).

Best Value CPU: Intel Core i5-11600K

  • Half the price of the i9-11900K, but still excellent performance at up to 4.9 GHz.

  • 6 cores / 12 threads: There are a decent number of threads to make it good at everyday multi-threading tasks, such as having tons of browser windows open.

  • Check the latest price of the Intel Core i5-11600K on Amazon (affiliate link).

  • Intel Core i5-11600KF (affiliate link) is a backup option if this one isn't in stock. It is the same other than the lack of integrated graphics support.

    Intel Core i5-11600K Intel Core i5-11600K Check Price on Amazon (affiliate link)
  • For the Intel Core i5-11600K CPU, you'll need a motherboard with the Z590 chipset to support PCIe 4.0.

  • Our recommended motherboard to pair with the i5-11600K is MSI's Z590 PRO WiFi ProSeries motherboard: MSI Z590 PRO WiFi ProSeries MSI Z590 PRO WiFi ProSeries Check Price on Amazon (affiliate link)

    • PCIe 4.0 support
    • Wi-Fi 6E makes it easy to reach the fastest speeds and future-proof your Wi-Fi system.
    • Bluetooth 5.2 (TR) is great for streaming music to Bluetooth headphones.
    • Three NVMe M.2 (TR) slots, which is pretty good! (Only one of them runs at PCIe 4.0 speeds)
    • Two 2.5 Gb Ethernet ports are faster than most Internet speeds with room to spare for file transfers.
    • USB 3.2 Gen 2x2 offers 20 Gbps USB speeds!
    • Check the latest price of the MSI Z590 PRO WiFi ProSeries on Amazon (affiliate link).

Learn More About PCI-Express

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Want to brush up on the latest PCIe products, versions, and features? Check out the articles in this PCI-Express series: