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Answered: Is PCIe Backward Compatible?

Learn about PCI-Express version and lane backward compatibility.

PCI-Express Kevin Jones / TechReviewer

Last Updated: December 28, 2021

Written by Kevin Jones

Are PCIe Versions Backward Compatible?

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PCI-Express 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

Check out my Recommended PCIe 5.0 CPUs and Motherboards below.

Are PCIe Versions Forward Compatible?

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PCIe versions are forward compatible, meaning that you can use a newer PCIe device with an older system. However, PCI-Express will use speeds based on the lowest of the two versions for communication.

Check out the table above to determine what the throughput limit would be for a specific configuration.

Multiple PCIe Versions for CPU/Motherboard

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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.

PCIe Slot Compatibility

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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.

Lane Availability

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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.

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Thinking of upgrading your CPU to support PCIe 5.0? Here are our recommendations:

Best Intel High-Performance Enthusiast CPU: Intel Core i9-12900K

  • Up to 5.2 GHz: perfect for games, video editing, and high-intensity tasks.

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

  • Virtualization features make it great for running virtual machines.

  • Check the latest price of the Intel Core i9-12900K on Amazon (affiliate link).

    Intel Core i9-12900K Processor 16 Cores (8P+8E) up to 5.2 GHz Intel Core i9-12900K Processor 16 Cores (8P+8E) up to 5.2 GHz Check Price on Amazon Amazon Affiliate Link
  • For the Intel Core i9-12900K CPU, you'll need a motherboard with the Z690 chipset to support CPU overclocking. Otherwise, you can use a motherboard with Intel's other 600 series desktop chipsets (e.g., H670, B660, H610).

  • Our recommended DDR4 motherboard to pair with the i9-12900K is Gigabyte's Z690 AORUS Elite AX DDR4: GIGABYTE Z690 AORUS Elite AX DDR4 GIGABYTE Z690 AORUS Elite AX DDR4 Check Price on Amazon Amazon Affiliate Link

    • PCIe 5.0 support
    • It supports up to 128GB of DDR4 memory!
    • 2.5 Gb Ethernet port is faster than most home Internet speeds with room to spare for file transfers.
    • Wi-Fi 6
    • Bluetooth 5.2 is great for streaming music to Bluetooth headphones.
    • Four x4 NVMe M.2 slots, which is fantastic! All four of these run at PCIe 4.0 speeds.
    • USB 3.2 Gen 2x2 offers 20 Gbps USB speeds!
    • Check the latest price of the GIGABYTE Z690 AORUS Elite AX DDR4 on Amazon (affiliate link).
  • Our recommended DDR5 motherboard to pair with the i9-12900K is Gigabyte's Z690 AORUS Master: GIGABYTE Z690 AORUS Master GIGABYTE Z690 AORUS Master Check Price on Amazon Amazon Affiliate Link

    • PCIe 5.0 support
    • It supports up to 128GB of DDR5 memory (DDR5 provides the fastest memory speeds)!

      DDR5 memory appears to be out of stock at most retailers, so I recommend sticking with a DDR4 motherboard or preparing for a long wait.

    • 10 Gbps Ethernet port is faster than any home Internet speed available with tons of room to spare for file transfers.
    • Wi-Fi 6E makes it easy to reach the fastest speeds and future-proof your Wi-Fi system.
    • Bluetooth 5.2 is great for streaming music to Bluetooth headphones.
    • Four x4 NVMe M.2 slots, which is fantastic! Three of these run at PCIe 4.0 speeds, and one at PCIe 3.0 speeds.
    • USB 3.2 Gen 2x2 offers 20 Gbps USB speeds!
    • Check the latest price of the GIGABYTE Z690 AORUS Master on Amazon (affiliate link).

Best Value CPU: Intel Core i5-12600K

  • Less than half the price of the i9-12900K, but still excellent performance at up to 4.9 GHz.

  • 10 cores (6 Performance + 4 Efficiency): This core count makes it suitable for everyday multi-threading tasks, such as having tons of browser windows open.

  • Virtualization features make it great for running virtual machines.

  • Check the latest price of the Intel Core i5-12600K on Amazon (affiliate link).

    Intel Core i5-12600K Intel Core i5-12600K Check Price on Amazon Amazon Affiliate Link
  • For the Intel Core i5-12600K CPU, you'll need a motherboard with the Z690 chipset to support CPU overclocking. Otherwise, you can use a motherboard with Intel's other 600 series desktop chipsets (e.g., H670, B660, H610).

  • Our recommended DDR4 motherboard to pair with the i5-12600K is GIGABYTE's Z690 Gaming X DDR4 motherboard: GIGABYTE Z690 Gaming X DDR4 GIGABYTE Z690 Gaming X DDR4 Check Price on Amazon Amazon Affiliate Link

    • PCIe 5.0 support
    • It supports up to 128GB of DDR4 memory!
    • Four x4 NVMe M.2 slots, which is fantastic! All four of these run at PCIe 4.0 speeds.
    • 2.5 Gb Ethernet port is faster than most home 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 GIGABYTE Z690 Gaming X DDR4 on Amazon (affiliate link).
  • Our recommended DDR5 motherboard to pair with the i5-12600K is GIGABYTE's Z690 AORUS PRO motherboard: GIGABYTE Z690 AORUS PRO GIGABYTE Z690 AORUS PRO Check Price on Amazon Amazon Affiliate Link

    • PCIe 5.0 support
    • It supports up to 128GB of DDR5 memory!

      DDR5 memory appears to be out of stock at most retailers, so I recommend sticking with a DDR4 motherboard or preparing for a long wait.

    • Three NVMe M.2 slots, which is excellent! These all run at PCIe 4.0 speeds.
    • 2.5 Gb Ethernet port is faster than most home 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 GIGABYTE Z690 AORUS PRO on Amazon (affiliate link).
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Due to the limited availability of DDR5, I'm only recommending a specific DDR4 product at this time.

However, you can check the current availability of DDR5 on Amazon (affiliate link).

  • It comes in a variety of frequencies, including 3000 MHz, 3200 MHz, 3600 MHz, 4000 MHz, and 4400 MHz
  • Reasonable CL16 timings (CAS Latency)
  • The low-profile form factor ensures that the heat spreaders don't get in the way of other devices, including your CPU heatsink
  • Crucial is a reputable brand, and I have used their memory in my machines
  • The customizable LEDs zones are a pretty cool bonus Crucial Ballistix RGB DDR4 Crucial Ballistix RGB DDR4 Check Price on Amazon Amazon Affiliate Link

Other Considerations When Building a PC

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Want to brush up on other new technologies to consider when building a computer? Check out these articles:

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: