PCI Express slot is basically rectangular that protrudes out of the motherboard and has many terminals on either side. PCI Express slots look different depending on their sizes, x1, x4, x8, and x16. The slot has two parts, the first one is constant across all slots and acts as the KEY and the second part varies depending on the PCIe lane count.
These slots will often be found on the part of the motherboard that is closest to the computer’s case IO shield. That’s because many expansion cards that go into PCIe slots expose some ports outside the computer.
For instance a graphics card has many video output ports that go out of the I/O shield and expose the video ports to the user outside of the case.
In this article we will explore the looks of the PCIe slots in detail, as looks do not always correspond to performance, particularly in the case of x16 slots.
So What Does a PCIe Express Slot Look Like?
The image above shows PCIe express slots. You can see here that the PCIe express slots are basically long rectangular slots with many terminals inside.
You can also notice that PCIe slots have different sizes. The larger the slot, the more PCIe lanes the slot often has.
An x1 slot is the smallest and it has a single PCIe lane. An x16 slot is the largest found on commercial boards and it can have the most amount of PCIe lanes.
If you are not aware of PCIe lanes, these are basically pipelines that deliver information to and from the PCIe slot (and the card attached to it) and the CPU. The more demanding the expansion card is, the more PCIe lanes it requires.
For instance, graphics cards are some of the most demanding expansion cards and generate a lot of data that need to be transferred to and from the card and the CPU.
Hence, they are designed for the largest x16 slots and are thus said to occupy 16 PCIe lanes. A Wireless Network card, on the other hand, merely requires an x1 slot.
The first part of the PCIe slot is constant. All the slots have this part. This first part ends at the ridge that’s also known as the hardware key. More on this below.
Its use is to ensure that only the right component is installed in the correct PCIe slot. Any other non-PCIe device won’t fit inside the slot thanks to this.
Also Read: How to Check How Many PCIe Slots Do I Have?
The Curious Case of the x16 Slot
x16 slot is the most versatile slot on the motherboard and also the most confusing. This is a slot that is designed to occupy large, heavy and high powered cards like graphics cards.
If your motherboard has a single PCIe x16 slot, which most do, then intuitively, it would offer 16 PCIe lanes.
However, if you have a second PCIe slot, then there are high chances that it would not offer the full 16 lanes.
The second PCIe x16 slot is often either an x8 slot or an x4 slot. Meaning, despite having a full x16 slot size, it would only feature 8 or 4 lanes.
You can figure out the exact lanes for a certain slot and through the spec sheet.
Have a look at the specs below for Gigabyte GA P67A UD3:
Read the numbers “1” and “2” PCIe slot description.
The “1” reads that the first PCIe x16 slot runs at x16 lanes.
The “2” says 1 x PCI Express X16 slot, running at x4. Hence, this is not suitable for demanding cards. If you were to put an NVIDIA Graphics card that requires at least an x8 slot.
NVIDIA GPUs require ATLEAST an x8 slot.
x16 Slot Clips
Another important point to note about x16 slots is that most of them have locking clips / latches at the end.
These latches and locks serve the purpose of securely holding the installed card in. Since, graphics card are often installed on x16 slots and since they tend to be heavy, these latches are all the more important.
Also Read: How to Unlock PCIe Slot Clip
The Fixed Part – Key
The first part of a PCIe slot, called the KEY, consists of eleven terminals on either side of the PCIe slot, making a total of 22 terminals.
The first part of the slot is consistent throughout all PCIe slot sizes. The most important purpose of this slot is power supply.
It measures about 11.65mm in length. The slot itself comes in at about 11.25mm in height from the mounting surface on the board to the top.
The remainder of the pins are variable and depends upon the size.
The Variable Part
The second part that comes after the KEY varies depending on the physical measurement of the slot.
The x1 slot is the smallest while the largest slot on mainstream motherboards is the x16. There is, however, an x32 slot as well, but it is uncommon on commercial motherboards.
The biggest factor that determines the size of the slot is the number of lanes it accommodates. That is, the higher the number of lanes on a slot, the larger the slot will be.
But this is not always the case since you can even find an x16 slot with only four lanes too as mentioned earlier.
To better understand what does a PCI Express slot look like, let’s go through the available slots.
This is the smallest slot on the motherboard in terms of physical lanes. It has only one PCIe lane and is good for smaller less power demanding expansion cards.
That said, the slot measures about 25 mm in length. On it, there are a total of 18 working pins, including the first 11.
Also Read: 10 Things That Can Be Plugged in PCIe Slot
This slot has four times the lanes in an x1 slot. However, it measures just about 39mm in length. The slot has a total of 32 pins inside.
Commercial motherboards mostly do not have a dedicated x4 slot. Instead, an x16 slot is repurposed into an x4 slot. These are often labelled as x16(x4) slots – meaning the slot has the physical size resembling an x16 slot, but it is only wired to 4 lanes.
The x8 slot is ideal for high bandwidth devices. That said, it has twice as many lanes as the x4 slot and is capable of taking even a graphics card.
It measures 56mm in length and has 49 pins in total including the first 11 pins.
Similar to the x4 slots above, an x8 slot on most, if not all, motherboards has the physical size of an x16 slot. These slots are often labelled as x16(x8) slots.
This is the largest slot on the motherboard and is used by devices that have the highest bandwidth requirements.
It offers the highest mainstream performance for any PCIe generation and it comes up at about 89mm in length.
With this, it houses as maximum of 82 pins. A true x16 slot offers 16 PCIe lanes and is mostly used for a graphics card.
Also Read: What Does a Motherboard Look Like?
What are Reinforced PCIe Slots?
Most PCIe slots are made entirely out of plastic. This is ideal for reducing the overall cost. However, on many high end motherboards, particularly on the gaming motherboards, you may find reinforced x16 slots.
These are basically built for holding and supporting large graphics cards that tend to be quite heavy.
The motherboard above, for instance, has a a single reinforced x16 slot.
It also has another PCIe x16 slot but it is not reinforced. Well that is because the second PCIe x16 slot has only 4 lanes is not intended to support graphics cards.
Certain motherboards for multi GPU support do have two reinforced x16 slots.
Image: Gigabyte X570 Aorus. The motherboard above has two reinforced PCIe x16 slots.
How Durable are PCIe Slots?
PCIe slots are durable enough to handle graphics cards that can weigh more than 5 pounds or 2.26 kilos.
The reinforced PCIe slots are designed to stay intact even if the PC takes an accidental fall.
Hopefully, this article makes it easier to tell what does a PCI Express slot look like. But, even for the newbies, these are not easy to miss.
These are some of the most essential slots when it comes to motherboard expandability. Whether you want to add a graphics card or a network adapter, you will need to know what PCIe slots look like and which one to use.
Different cards have different PCIe lanes requirements and are hence designed for corresponding PCIe slots.
In terms of physical looks, they are mostly made out of plastic and have pins on either side of the slot, however, on certain motherboards you may find reinforced x16 slots made out of steel. The KEY notch ensures that only PCIe devices are installed in the PCIe slot.
In general PCIe slots are located next to the I/O shield since the cards that plug in often have some parts or ports exposed outside the case.