What Does PCIe x16 Mean?

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PCIe x16 is a slot on a motherboard that has 16 data links known as PCIe lanes. This is a slot with the highest throughput rate and can be occupied with expansion cards that have a very high bandwidth requirement such as graphics card.

Modern motherboards in desktops are highly customizable. If you have a motherboard, you can install more components on it to get better performance out of it.

The two key interfaces through which you add components to your system are the SATA and the PCIe interfaces. The SATA interface is more or less designated for components that have very low bandwidth requirement such as hard disk drives.

For high speed devices, however, you use the PCIe interface. There are different version of PCIe interface and the motherboard can have different sizes of PCIe slots too.

If all this sounds too confusing to you, it is fine. PCIe is not something that you can understand on the first glance. The only key point, you need to remember at the moment is that PCIe is a standard used for modular expansion of your PC.

Among the PCIe standard, x16 slot is the largest slot and offers the highest throughput rate on a consumer grade motherboard. In this article, we will further explain what does PCIe X16 mean.

Also Read in Depth:

What Does a PCIe x16 Slot Look Like?

What Does PCIe x16 Mean

Image: A typical x16 slot.

The PCIe x16 is the largest slot found on a motherboard.

A true x16 slot with 16 lanes measures 89 mm in length and has 82 pins, each of which serves a certain purpose such as providing power and transferring data.

In contrast to this, the smallest slot, PCIe x1, has 18 pins and measures 25mm in length.

PCIe slots motherboard 2

Image: In the image above, the white slots are x1 slots and the blue slots are x16 slots.

What is the x16 Slot Used For?

Image: Graphics Cards go into the x16 slots.

An x16 with 16 PCIe lanes is almost always used by your primary graphics card.

This is because graphics cards generate the most amount of data and they ideally require a slot with the highest bandwidth – which is x16 on a commercial motherboard.

What Does the “16” after “x” Mean Here?

In most cases, the number after “x” denotes the amount of PCIe lanes the slot has. For instance, an x1 slot has a single PCIe lane, an x4 has four lanes and so on.

However, in the case of x16 slots, the number “16” DOES NOT ALWAYS pertain to the amount of lanes on the slot, we will read about that further below.

But in order to understand the purpose of the x16 slot and how they are configured, you need to understand PCIe lanes, PCIe version and the different slots available.

PCIe Lanes and Version

PCIe lanes are data links or pipelines through which data is transferred from the PCIe slot to CPU.

The amount of PCIe lanes you have on a particular PC are limited and the total amount you have depends upon your CPU and the motherboard chipset.

An average consumer grade CPU provides 16 dedicated PCIe lanes and and an average motherboard provides about 4 dedicated PCIe lanes.

Therefore, with a configuration like this, you can get 20 dedicated PCIe lanes. So here you could have one possible build with a graphics card taking up 16 lanes and an SSD expansion card taking up the other 4 lanes.

Depending upon your use case and how the motherboard slots are configured, you can have different types of builds.

Also Read: How to Check How Many PCIe Lanes Do I Have?

A very important factor regarding PCIe interface is its version. The latest motherboards at the moment feature the PCIe v4.0, however, it is not uncommon to find motherboards with PCIe v3.0 and even PCIe v2.0. PCIe v5.0 is also just around the corner.

The key point to note is that every new PCIe version doubles the per lane throughput compared to the previous version. So a PCIe v4.0 x16 slot is twice as fast as the same slot conforming to the PCIe v3.0 interface.

This is very significant because with a higher throughput rate on the newer version, you can install faster and better expansion cards.

The following table summarizes the throughput rate of various versions.

Versionx1
(GB/s)
x2
(GB/s)
x4
(GB/s)
x8
(GB/s)
x16
(GB/s)
1.00.2500.500 1.0002.0004.000
2.00.5001.0002.0004.0008.000
3.00.9851.9693.9387,87715.754
4.01.9693.9387,87715.75431.508
5.03.9387,87715.75431.50863.015
6.07.87715.75431.50863.015126.031

Also Read: What are Motherboard Standoffs?

PCIe Slots and Its Types

Before we get down to discussing PCIe x16 slot, there are other PCIe slot sizes that we need to mention.

This will give you a much clearer idea about what PCIe x16 slot pertains to.

Each PCIe slots has its purpose. Smaller PCIe slots, such as x1 slots, are suitable for expansion cards that generate a lower amount of data i.e WiFi Cards, Sound Cards etc.

Also Read: 10 Things that Can be Plugged in PCIe Slots

PCIe x1 Slot

This PCIe slot type has the smallest physical slot size. Additionally, it has the least bandwidth due to it having only one PCIe lane.

x1 is used for low demanding cards like modems, sound card, port expansion cards etc.

Also Read: What are PCIe x1 Slots Used For?

PCIe X4 Slot

At four times the size of the smallest PCIe slot, this slot has 4 PCIe lanes.

This is excellent for cards that require a higher bandwidth like NVMe SSD expansion cards, 10G Network Cards, among others.

PCIe X8 Slot

An x8 slot is often used for a second graphics card. If you have a PC with dual NVIDIA graphics cards, the second graphics card is plugged into the x8 slot.

Besides that, the x8 slot can also be used for RAID controllers.

So What Does PCIE X16 Mean?

does it matter which PCIe slot I use

Image: There is a difference between x16 and True x16 slots. Sometimes a slot that may have a physical size of an x16 slot may only have 8 or even 4 lanes. In the motherboard above, the second x16 slot has only 4 lanes

There is a difference between x16 slot and a True x16 slot as can be seen in the image above.

We can see that the Gigabyte GA-P67A-UD3 has two PCIe x16 slots, as far as the physical size is concerned.

However, only the top slot is a True x16 slot. The second one on the bottom only has 4 lanes and hence it would not be suitable for installing graphics cards.

However, since PCIe slots are cross-compatible, you can install smaller x4 cards, like an NVMe SSD expansion card, into the bottom x16(x4) slot instead.

The True PCIe x16 slot with 16 lanes is the largest and the fastest slot found on consumer grade motherboards. Hence, it is currently THE primary slot used for graphics cards.

Also Read:

Devices Used on PCIe X16

nvidia rtx 2080

Image: x16 is primarily used for graphics cards

An x16 is primarily used for graphics cards. If you have a single graphics card, you must plug it into the True x16 slot with 16 lanes.

If you have two PCIe x16 slots on your motherboard, make certain that you do not plug the card into the x16 slot with a lower lane count as we saw earlier with the case of Gigabyte GA-P67A-UD3 motherboard where one of the x16 slot had only 4 lanes.

SLI MOTHERBOARDS: Do note that if you have a motherboard for SLI (Dual NVIDIA Graphics Card) with two x16 slots, then occupying both slots with a graphics card will dial both of them down to x8 lanes only. This is because the amount of lanes you have on your system are limited so motherboard have to distribute the lanes.

Also Read: Why is Second x16 Slot in SLI PCIe x8?

With that said, due to the cross and backward compatibility of the PCIe interface, most PCIe devices can be used on any PCIe slot as long as they can fit.

This means that you can install any other device be it a network card, video capture card, SSD expansion card etc into the x16 slot.

Of course, if you install a smaller card on an X16 slot, you will be sacrificing the precious high throughput slot.

Will a PCIe X1, X4 or X8 Card Work Faster on X16 Slot?

The answer is a resounding no.

While the x1, x4, or x8 cards will certainly work just fine on an x16 slot, they will not gain any type of performance boost.

Final Words

Basically, in order to understand what does PCIe x16 mean, you need to learn some basics regarding the PCIe interface such as the different slots, PCIe lanes and the version.

In the simplest of terms, the x16 is the largest readily-available size for any PCIe version on the consumer grade motherboard.

Since it offers the highest bandwidth, it is generally used for expansion cards that require highest bandwidths such as graphic cards.

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Author:

Atif Qazi
Atif Qazi is the founder of PCGuide101. He is a digital nomad who loves everything PC. He is a PC builder, tech enthusiast, engineer, and a lover of single player lore-rich RPG games.

2 thoughts on “What Does PCIe x16 Mean?”

  1. I’m looking at the TUF GAMING B550M-ZAKU (WI-FI)
    90MB15P0-M0AAY0
    For amds crossfirex / multi graphics card but I don’t know if there’s much better buys and what would be a good graphics card to run 2 of

    Reply
    • The answer to your question mostly depends upon your budget, particularly when you ask me for recommendations regarding the graphics cards to go for.

      As for the motherboard, I would not recommend this for SLI or Crossfire (unless you are okay with performance loss). Why? The second PCIe x16 slot not only has only 4 lanes, but those 4 lanes conform to the PCIe v3.0. Only the primary or the top PCIe x16 slot offers 16 lanes conforming to PCIe v4.0. Thus, the second PCIe x16 slot can bottleneck your graphics card.

      How much of a bottleneck you experience would depend upon the your graphics card. High end GPUs would suffer a higher performance loss on an x4 slot compared to a lower end GPUs.

      In case of cross-firing mid and high end GPUs, you will probably need to look into the X570 chipset i.e check out ASUS Prime X570-Pro motherboard. It’s expensive, but great if you want to crossfire two mid range or high end GPUs.

      Reply

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