Can You Plug A PCIe X1 Into an X16 Slot? – Can it Work?

The short answer is yes. You can plug a PCIe x1 card into the larger PCIe x16 slot. A PCIe x1 card can be plugged into any larger PCIe slot and it will work just fine. Whether this is advisable or not is another question which we will explore below.

There are a few challenges to overcome when building or upgrading a PC. One of them is knowing what goes where especially when it comes to a standard such as PCIe which has different-sized ports and a wide range of components.

So, if you’re wondering can you plug a PCIe x1 into an x16 slot, read on to find out why that is an affirmative. PCIe standard is not only cross compatible but also backwards compatible.

The choice of the slots you use for your cards is an essential consideration of your overall build.

PCIe Slots and Their Sizes

let’s have a brief overview of the PCIe slot sizes. There are basically 4 different PCIe slot sizes (in terms of their lane count), x1, x4, x8, and x16. The number after the “x” represents two characteristics i.e size and lane count.

It should be noted here that not all x16 slots have 16 lanes. If you have a two x16 slots then there are high chances that the second would only have 8 or even 4 lanes.

Image: the Blue Slots are x16, the White Slots are X1 slot.

What are PCIe lanes?

Well, PCIe lanes are the pipelines that deliver information to and from the PCIe slot and the devices connected to it. Every PCIe expansion card has a certain lane requirements. The more lanes a slot, the higher is its throughput rate (speed).

Also, your PC only has a limited amount of PCIe lanes. They are determined by the CPU and the motherboard chipset model you have.

We recommend brushing up your knowledge on PCIe lanes and slots:

So Can You Plug A PCIe x1 Into An x16 Slot and Will it Work?

You can most certainly plug a PCIe x1 card in a PCIe x16 slot. This is is due to the PCIe design which allows cross compatibility.

As discussed earlier, PCIe x1 slot has just one PCIe lane. It also happens to be the smallest PCIe slot on motherboards.

On the other hand, we have the x16 PCIe slot. Unlike the x1, this one has whopping 16 lanes. This slot happens to be the largest slot found on consumer motherboards.

The higher the lane count, the higher would be its throughput rate. An x16 slot can handle the data transfer rate of very powerful devices like a graphics card.

An x1, slot on the other hand, can handle cards that do not have a very high data transfer rate such as network adapters.

So What is PCIe Cross and Backward Compatibility?

PCIe cross compatibility means that not only can a PCIe x1 card fit in an x16, it can also fit in x4 and x8 slots. Similarly an x4 card can also fit in x8 or x16 slots.

1.00.2500.500 1.0002.0004.000

Table: PCIe version, lane and their corresponding speed.

Backward compatibility means that a PCIe v3.0 device can fit into a PCIe v2.0 slot, and vice versa, albeit the expansion card will operate on the slower speeds of the two.

Also, there is no danger of physical damage if you install a smaller card in a bigger slot. While an x16 slot may be larger than the PCIe x1 connector on the card, with a firm fastening in the motherboard, your card will barely move around.

This is because all PCIe cards have a standard retainer screw that affixes the PCIe card to PC chassis.

Of course, plugging in a PCIe x1 card into a PCIe x16 slot, you bring up a few demerits that need to be addressed. These won’t hamper the performance of the card, but for the overall build, it can present an issue.

Also Read in Detail: Is PCIe Backward Compatible?

Drawbacks and Demerits of Plugging in a PCIe x1 Card in an X16 Slot:

While you CAN install an x1 card into an x16 slot, it is not advisable. The following are the reasons why:

1. Performance Isn’t improved Despite More Lanes

The first is that the x1 card will not perform any better on an x16 slot with its 16 lane speed.

What this means is that while the PCIe x16 (version 3.0) slot has a throughput (speed) of 15.754 GB/s, the X1 card will not go overdrive to push out that much data. It will still be limited to its designed throughput.

Most PCIe x1 cards aren’t even designed to meet the throughput of a single PCIe lane let alone 16 of them.

Take a PCIe WiFi 6 Network card for instance. The nominal throughput of these devices is 2.4 Gbps or 300 Megabyte per second. This is far less than the 985 Megabyte per second supported throughput rate of a PCIe x1 slot (version 3.0).

Also read: Which PCIe Slot for Wireless Card?

As mentioned earlier, the PCIe interface only runs at the fastest speed of the slowest component, and if the x1 card can only do 300 MB/s max then that is the speed that the slot will run on too. Not higher.

2. Wastes Resources

Another drawback is that having an x1 card in an x16 slot can be a grand waste of potential.

You see, an X16 slot is designed to be the fastest on the motherboard depending on the PCIe generation it is from.

And as seen, the interface gets handicapped by the slowest component in use. So, if you put two and two together, you see that at the very least, fifteen whole PCIe lanes will go unused and that is a very costly waste of resources, especially for a computer.

The X16 slot is meant for beefier cards that require large data throughput, like graphics cards. But, putting in an x1 card, like a port expansion card, in that slot may not be the best idea.

3. PCIe Slots are Limited

The fact that PCIe slots on a motherboard are limited further cements the point of wasting resources.

Many motherboards only have one PCIe x16 slot and it’s usually intended for the graphics card.

Also Read:

Having Extra PCIe Slots

How to Add More PCIe Slots
Image: An example of a PCIe Riser that splits a single x4 slot to multiple x16 slots (it does not increase the overall throughput of the x4 host slot)

If you have an extra PCIe x16 slot to spare, but have multiple smaller cards that you want to install, you can get PCIe Riser, aka splitter, to add more slots to your system.

The extra slots will not increase the amount of PCIe lanes you get, it will, however, help in bifurcating the throughput of a single x16 slot to multiple slots.

Read this article for details regarding PCIe splitter: How to Add More PCIe Slots?

Final Words

PCIe is a protocol that is highly cross and backward compatible. You can not only plug an x1 slot in an x16 slot, but also in x8 and x4 slots. Similarly you can install an x4 card in x8 and x16 slots as well.

The cards can vary across generation, but they will still work (at the speed of the lowest component i.e slot or the card).

While we do not recommend occupying an x16 slot with a mere x1 card because you will wasting resources, there are certain times where this arrangement may be needed for instance if you have no smaller x1 slots available.

Also Read: Difference Between PCIe x1 and x16

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Atif Qazi
Atif Qazi is the founder of PCGuide101 and an expert in the computer peripheral industry with over two decades of experience. He has worked as a consultant for major companies and has a deep understanding of the inner workings of computer peripherals. He has a degree in Electrical Engineering and has served as a product manager and technical consultant. He is passionate about testing and evaluating the latest products to provide readers with reliable information.

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