PCI Express 2.0 X8 Vs X16

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A companion piece was requested to describe the differences between PCI Express 2.0 X8 Vs X16. We are pleased to answer any inquiries that customers may have (Please contact us if you have any inquiries about industrial computers).

Comparison Between PCI Express 2.0 X8 Vs X16

Comparison Between PCI Express 2.0 X8 Vs X16

A connection with more data lanes has more bandwidth between the card and the host. Higher lane counts, on the other hand, usually mean higher costs. The PCIe protocol is a newer version of the PCI protocol. PCIe was created for peripheral component connections, similar to PCI/PCI-X. PCIe differs from PCI/PCI-X in various ways.

However, most of those differences are beyond the scope of this blog. However, one significant distinction will help us better comprehend the distinctions between the PCIe protocol versions (x1, x4, x8, x16, and x32). The essential distinction is between ‘parallel’ and serial data transmission.

All of the cards in a PCI or PCI-X architecture share parallel data lines to and from the host. Data speeds are frequently throttled due to differences in card speeds and slot kinds.

Each card has its own dedicated serial data connections (lanes) to the host in the PCIe architecture. This allows each card connection to attain its bandwidth, regardless of other cards in the system. The suffix of the PCIe protocol (1, 4, 8, 16, 32) indicates the number of lanes. Depending on the version of the PCIe protocol, each lane can reach rates of 250-1969 MB/s (v1.x, v2.x, v3.0, v4.0).

PCIe cards can always be used in PCIe slots that have the same number of lanes as the card. An x8 card, for example, can be used in a slot with x8, x16, or x32 lanes. An x1 card can also be used in any PCIe slot.

Is It Possible To Use A PCIe X8 Card In An X16 Slot?

A PCIe X8 card will undoubtedly fit in an x16 slot. However, the card’s bandwidth will be limited to 8 PCIe lanes. In other words, the installed card will not use all of the X16 lanes available in the slot. A lot can be added or modified on the motherboard thanks to the two key user-accessible interfaces, PCIe and SATA.

While SATA is mostly utilized for storage drives, the PCIe interface is responsible for HSIO (High-Speed Input Output) devices. PCIe slots come in various sizes, including X1, X4, X8, and X16, and each has its performance and bandwidth specs. The success of the PCIe interface is due to its ease of use, modularity, and cross-compatibility. A smaller card can be inserted into a larger slot and vice versa.

As a result, the answer to the query “can PCIe X8 card fit in X16 slot?” is yes. Another concern is if you SHOULD install a smaller card or a larger slot. In the material below, we’ll go over the entire idea of this topic.


The PCIe X8 slot is unusual in that it can be difficult to distinguish from an X16 slot when looking at a motherboard. The X8 and X16 slots on consumer-grade motherboards will have identical physical sizes. As a result, simply looking at the physical profile will not reveal which slot it belongs to.

Instead, you should consult your motherboard’s spec sheet to determine the correct information about your PCIe slots. There are fewer terminals on an X8 slot that is the same size as an X16 slot. This also means fewer lanes will be available to transfer data, resulting in reduced bandwidth.

Can PCIe X8 Fit In X16?

The obvious slot to look for if you have a peripheral device with a PCIe X8 connector is an X8 slot. Unfortunately, most, if not all, commercially available motherboards lack this slot. Instead, an x16 slot may be available if you ask if an x8 card will fit in an x16 slot and function.

Why? The benefit of the PCIe standard is that most devices and slots are interchangeable. Installing an X8 card in an X16 slot, on the other hand, will allow you to utilize the card’s capabilities fully. There are a couple of caveats, though:

The PCIe Version Matters

It’s good to double-check that the add-in card and the slot are from the same PCIe generation, such as PCIe 3.0 or PCIe 4.0. This is because various generations, while cross-compatible, have significant performance differences. For example, sliding an X8 PCIe 3.0 add-in card into an X16 PCIe 2.0 Slot may not perform as well since the PCIe interface operates at the slower of the two speeds.

So, if you have a PCIe v4.0 device, it will reduce its performance to that of a PCIe v2.0 device. It’s worth mentioning that each subsequent PCIe generation doubles the previous one’s throughput rate (speed). So, on PCIe version 2.0, a single lane has a throughput rate of 0.5 GB/s, while versions 3.0 and 4.0 have 0.985 GB/s and 1.969 GB/s, respectively.

The Card Will Not Use All 16 Lanes

While an x8 device can be installed in an x16 slot, the device will only use 8 of the slot’s lanes. The remaining eight lanes will be useless. So, the point is that you may have squandered a larger slot that could have been used for more demanding cards like a graphics card.

No Performance Gains

There will be no performance increases because just eight lanes of the x16 slot will be used. In other words, the card’s throughput rate will be limited to 8 lanes rather than 16.

What To Do If Your Motherboard Only Has One X16 Slot?

When you have a motherboard without an X8 slot but just one huge X16 slot, such as the Asus Prime B460M-A, you must select whether to use your x8 add-in card in the slower X4 slots or the considerably faster X16 slot if it is empty.

Certain add-in cards allow you to choose how many PCIe lanes you require. For example, AMD Radeon Graphics Cards function best in an x16 slot, but they can also work in an x8 (at a slightly lower performance) or even an x4 slot (at a much lower performance).

So, if you have an x8 device and want to use the X16 slot, the card will work fine as long as the slot is AT LEAST the same PCIe version as the add-in card, if not better. While an X16 slot has more lanes than an X8 slot, you won’t necessarily profit from the extra lanes; however, the card will perform at its maximum capacity.

Installing the identical device in an x4 slot, on the other hand, may function, albeit at a significantly reduced performance. Furthermore, the smaller x4 slot will need to be open-ended to accommodate the connector.]


In certain cases, such as the GTA V 58.3 vs 58 FPS output, the numbers are nearly enough to be practiced inside the test error margin and don’t reveal a performance difference. When a realistic performance disparity is displayed, such as the 1% difference in Metro: Last Light numbers, it is unnoticeable to the user but measurable using our methods. We’re talking 96FPS vs 95 FPS for Metro, and we mean unnoticeable.

By the way, Metro is the most trustworthy FPS benchmarking tool we’ve ever used. We trust these measures as being outside of test variance because the game produces nearly identical AVG, 1 percent low, and 0.1 percent lows with each test pass.

The speed difference between PCI Express 2.0 X8 Vs X16 slots appears to be less than 1%. Users concerned about potential slot or lane constraints should disregard the difference as insignificant.

We’re not sure how this works with SLI (especially MDA’mode’) or dual-GPU cards, but we’ll investigate once we get more gear in the lab. We’re also looking into how PCI-e lanes affect VRAM cards with lower capacities, such as 4GB. System resource constraints may put extra strain on the interface.

Frequently Asked Questions

Can a PCI Express x8 slot be used in an x16 slot?

A PCIe X8 card will undoubtedly fit in an x16 slot. However, the card’s bandwidth will be limited to 8 PCIe lanes. In other words, the installed card will not use all of the X16 lanes available in the slot.

Is x16 superior to x8?

When using two Titan X cards in SLI, the results are not nearly constant as when using a single GPU. Running at x16/x8 was the fastest at 1080p, beating x16/x16 by roughly 10%. Likewise, x8/x8 was slightly quicker than x16/x16, but only 8%.

Is x16 the same as PCI Express 2.0?

No, PCI-E 2.0 is also x16; the difference is that the theoretical bandwidth per lane is twice as great as PCI-E 1.1. It may seem like a most, but the vast majority (if not all) of today’s GPUs work similarly with 1.1 and 2.0.

PCIe x8 slots are used for what?

PCIe (peripheral component interconnect express) is a high-speed component interconnection standard. Several PCIe slots are available on every desktop PC motherboard for adding GPUs (also known as video cards or graphics cards), RAID cards, Wi-Fi cards, or SSD (solid-state drive) add-on cards.

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