What does a PCIe slot look like?

Building a PC when you are just starting out can be frustrating. There are a lot of things to look out for when picking out the parts for your desired build. You want it to be versatile and future-proof but also affordable.

When you are getting down to actually build the PC, setting up the motherboard can be one of the more difficult tasks. There’s a lot of work involved such as: installing the CPU (see also how to remove CPU from a motherboard), setting up standoff screws, etc.. One of these situations involves installing the GPU and/or other expansion cards into the PCIe slots.

So a newbie might have no idea what does a PCIe slot look like. To some people, motherboards are just an incoherent jumble of tiny resistors and electronic components that makes no sense. Because of this, trying to find the proper PCIe slot can become difficult.

The PCIe slots are the horizontal slits that protrude out from the motherboard and have small terminals on either side. They are situated just to the bottom left of the motherboard, slightly below the I/O panel. This is where the GPU is fixed on to the motherboard.

However, this is just a brief introduction to the PCIe slot, and in most motherboards there are several PCIe slots with different applications. Knowing about their capabilities and compatibility will help you in the long run as they are not just for GPUs. In the following sections I’ll go over some important information regarding PCIe slots such as

• What is their primary function?
• What are the different types of PCIe slots?
• What are the components that use PCIe slots?
• How to find the proper PCIe slot.

With that being said, I hope your thirst for the PCIe “knowledge” isn’t sated yet. So let’s dig deeper into the PCIe slot.

What is the primary function of PCIe slots and what does a PCIe slot look like?

PCIe stands for Peripheral Component Interconnect Express. As of right now, this is the fastest interface for transferring data to the CPU. Like most interfaces, the PCIe slot is used to connect another external or peripheral device to the motherboard, since they are not a part of the motherboard itself.

PCIe slots consist of “lanes” that act as a two-way street. There are two destinations for each PCIe lane, either they go directly to the CPU or they go to the motherboard chipset. Inside each lane there are two pathways, one for data transmission and the other for receiving data.

You might have already come across motherboard specs for the PCIe slot where they designate some PCIe slots as x16, x8, x4 and x1. Also, if you look closely at these designated slots you will realize that the x16 slot is the longest and the x1 slot is the shortest. The “x” in this case refers to the amount of lanes that the PCIe slot can support. The bigger the lanes, the faster the data transfer.

The CPU and GPU are one of the most fundamental components in any PC build. Therefore, you need a strong pathway between these two in order to exchange information as fast as possible. Otherwise, you won’t get to enjoy that sweet sweet 144Hz 1440p gaming experience as everything will be much slower to render. The PCIe lanes are responsible for this exchange and therefore, in order to transfer more data simultaneously, they utilize several lanes instead of one. Most modern GPUs use the largest PCIe x16 slot (with 16 lanes) to transfer the most amount of data in a very short time.

To give you a small idea of how fast PCIe lanes are, each lane can transfer 984.6 MB/s. Too bad we can’t use them in our flash drives, life would have been so much faster.

What are the different types of PCIe slots?

I mentioned previously that most PCIe slots located in the motherboard are categorized by the amount of lanes that they support, this is just one of the ways in which we can categorize PCIe slots. We can also group them by the type of components that are compatible with each slot and with the PCIe version.

Depending on the number of lanes that each PCIe slot consists of, we’ve got the x16, x8, x4 and x1 slots. Now the great thing about PCIe slots is that, in terms of the number of lanes, we can use a card that requires a smaller amount of PCIe lanes on a slot that has a higher amount of lanes, for example: we can use a network card that only requires x1 lanes on a PCIe x8 or x16 slot. They will work perfectly fine, since they already have more than enough PCIe lanes.

This can work the other way around also. So if you have a GPU that supports PCIe x16 it is also compatible in the PCIe x8 slot, provided that the x8 slot has enough lanes to physically hold the GPU. The underlying issue here is the bandwidth. Although you can use a GPU such as this on an x8 or even an x4 PCIe slot, the bandwidth capabilities of the PCIe slot will be severely underutilized, and you may not be able to use the GPU at its maximum potential.

Another property that affects the efficiency is the PCIe version. As of right now we have the recent PCIe version 4.0 for the latest GPUs, which is two times faster than its predecessor, the PCIe 3.0. Unfortunately, in order to take full advantage of PCIe 4.0 you need the motherboard, CPU and the GPU to be fully PCIe 4.0 compatible. So whenever you have the chance, try to upgrade to be PCIe 4.0 compatible.. Everything will be faster, even M.2 SSDs. (if they are PCIe 4.0 compatible)

What are the components that use PCIe slots?

Speaking of SSDs, there’s a ton of equipment that uses a PCIe slot in order to interface with the motherboard, let’s run through a few of the most common parts that are connected via PCIe.

GPU: This is the most obvious and widely used. Since GPUs transfer a lot of data between the CPU, especially when there’s gaming or rendering involved, most modern GPUs require x16 lanes that are directly connected to the CPU. You can easily spot the x16 slot as it is the one which is closest to the processor.

M.2 NVME SSD: The second most widely used component. SATA SSDs are fast, no doubt about it, but PCIe SSDs such as the M.2 NVMe SSDs are much faster than SATA SSDs. These M.2 SSDs also have a smaller form factor and they usually require the x8 or x4 lanes..

SATA expansion card: Depending on your requirements, you might run out of SATA ports and you may even need to set up a larger storage system or a RAID configuration. If that is the case, you can’t get more SATA ports by another SATA port, so you will have to resort to using an x4 PCIe slot. If you’re unsure of how many SATA ports you have and what a SATA port looks like, we’ve written articles that cover those topics.

Network Adapters: The old days of setting up LAN cards via PCIe are long gone. Most modern motherboards have Gigabit Ethernet ports, so LAN is not a problem. The modern problem is getting Wi-Fi, especially when some motherboards do not support Wi-Fi and bluetooth. For this reason, you can easily install a Wi-Fi adapter to the motherboard via the PCIe slots. Most often you would have to use the x4 or x1 lanes for these, depending on the speed of the network.

There are a ton of other various expansion cards such as sound cards, video capture cards and USB expansion cards.etc.. These are somehow rendered obsolete because modern motherboards already provide sound, in-built graphics and enough USB ports that will cater to most casual PC users.

How to find the proper PCIe slot?

So now, you’ve had your fair share of “knowledge” on what a PCIe slot does and what it’s used for. Let’s get into the more hands-on approach on how to identify a PCIe slot and how we can use them.

You might also be interested in this article about what are PCI-E x1 slots used for.

First, set up the motherboard such that the rear I/O panel is in the top left side. Then trace your finger down the CPU socket until you reach a large horizontal slit that’s protruding from the motherboard. If it’s an x16 slot you can identify it by the lock tab on it’s right edge, otherwise, it will be an x8 slot and shorter in length, likewise you can easily find the smaller PCIe slots (x4 and x1) in the same region, either above or below the largest PCIe slot. 

Conclusion

As a first timer, you may not be able to find it at first glance but after you do, PCIe slots start to stick out like a sore thumb. The first thing I look for, when I’m checking out motherboards, is to always check how many PCIe slots it provides. This amount of PCIe slots are a good indication of how versatile the motherboard is going to be. So even if it doesn’t provide in-built Wi-Fi or some other feature, you will always have the ability to add these features via a PCIe slot.