Modern motherboard desktops are highly customizable. If you have a motherboard, you can install more components on it to get better performance out of it.
While different components like RAM and CPU go into very specific ports, different PCIe devices can go into any PCIe slot; depending on the physical size of the device of course.
For this reason, we get a backward-compatibility of PCIe devices across different slot sizes and different PCIe versions.
If all this sounds too confusing to you, it is fine. PCIe is not something that you can understand on a 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 is an X16 slot. In this article, we will specifically look at what does PCIe X16 mean.
Basically, PCIe X16 is a slot size that give 16 PCIe lanes and thus the highest bandwidth, or transfer speeds, on a consumer grade PC.
Also Read in Depth: What are PCIe Slots?
Brief History of the PCIe Standard
Ever since its introduction in 2002, the PCIe slot has served to connect multiple high-speed devices to the motherboard.
Because it was faster than its predecessor (PCI) and offered more bandwidth, PCIe quickly became the norm for computer motherboards.
PCIe offered much higher bandwidth to the connected components. Therefore, many newer and powerful devices could be connected to the motherboard.
Most PCIe devices are compatible with the different versions of PCIe slots available making PCIe one of the most versatile connections on a motherboard.
Also Read: What is a Motherboard?
Types of PCIe Slots
Before we get down to discussing PCIe X16, there are other PCIe slot configurations that we need to mention.
This will give you a much clearer idea about what PCIe X16 slot pertains to.
These are somewhat less performant than the latter in terms of maximum bandwidth but still offer great benefits when used with compatible expansion cards.
PCIe X1 Slot
This PCIe type has the smallest physical slot size. Additionally, it has the least bandwidth due to only one PCIe lane.
Its size makes it difficult to use it with a device of PCIe X4 connector and above but you can go around this and install it even if the slot is open-ended – an open ended slot does not have a stopper in the end so the larger device can fit.
In this configuration, the larger and more demanding device will only work with one lane which may not be very ideal.
X1 is generally used for modems and networks cards.
PCIe X4 Slot
At four times the size of the smallest PCIe slot, this one has 3 more lanes than X1. This essentially gives you almost four-times the bandwidth you’d get with a PCIe X1 slot.
This is excellent for RAID Controllers or SSD expansion cards.
PCIe X8 Slot
For most devices, this slot can offer great performance. It has an 8-lane wide channel that gives you twice the bandwidth of a PCIe X4 slot.
In addition to that, it has twice the size of the slot as well.
It is also the most peculiar since it is rare to find an X8 sized slot on motherboard. Most X8 slot are instead found with the physical size of an X16 size.
These are generally used for graphics card in SLI or Crossfire configuration i.e two cards.
So What does PCIE X16 mean?
Having discussed the first three PCIe sizes, we can conclude that the number that comes after the ‘X’ refers to the amount of lanes a PCIe slot offers.
The number that comes after ‘X’ DOES NOT necessarily refer to the physical size since you can find X16 size slots with only X4 or X8 bandwidth.
If PCIe lanes were like roads, then an X16 PCIe would be like a 16-lane highway.
For every single cycle you can transmit much more data than you ever could with any of the other three configurations we saw above.
PCIe X16 slot is the largest slot found on consumer grade mothers. This is currently THE slot used for graphics cards.
Since graphics cards are powerful expansion cards, they require the highest bandwidth and thus the highest transfer speeds available. This is only possible with an X16 slot.
Size, Pin Count and Lane Count
As you can expect, the PCIe X16 slot is the largest in size of the three. It measures 89 mm in length and has 82 pins, each of which serves a certain purpose with some being left unused in some applications.
In contrast, PCIe X1 has 18 pins and measures 25mm in length.
Data across an X16 slot is transmitted through 16 lanes. The lanes consist of two pairs of conductors where one pair acts as a transmitter, sending data out of the device while the other pair acts as a receiver.
How Many Lanes Do You Have?
PCs do not have unlimited PCIe lanes. The amount of dedicated Lanes you have available are dictated by your processor as well as the motherboard chipset.
An average consumer grade processor provides 16 dedicated PCIe lanes and and average motherboard provides about 4 dedicated PCIe lanes.
Therefore, with a configuration like this, you can get 20 dedicated PCIe lanes. You can use this for a single PCIe X16 with an X4 RAID controller or SSD expansion card to complete the 20 total lane count.
You CAN have two graphics card installed as well, however, when installing two graphics card on a system with mere 20 PCIe lanes, the graphics card will be dialed down X8 each. Otherwise, you will need a PC with at least 32 PCIe Lanes to dedicate X16 to each.
X16 Speed across Different Versions
Several versions of PCIe exist and have been used in different motherboard models overtime. Older versions are rare these days but with an old computer, you may still find them in use.
For PCIe 1.0, the X16 slot can get you speeds of up to 4000 MB/s. This at the time was excellent for storage as it alleviated many bottlenecks that resulted from slow drives.
Moving up a generation to PCIe 2.0, we get almost double the speed of the previous generation, around 8000 MB/s.
The third generation, PCIe 3.0 is almost twice as fast as the previous generation but falls off just a little. Nevertheless, at about 15754 MB/s, this slot is great for many applications including some high-end graphics cards.
At 31504 GB/s, PCIe 4.0 is the latest version available in the market right now. It provides some of the best speeds that a PCIe 16X slot can take. While it is fast, it is not the fastest. We are sure to see more versions of PCIe releasing in the coming years with speeds doubling still.
Devices Used on PCIe X16
Due to their high compatibility, most PCIe devices can be used on any PCIe slot as long as they can fit. They are mostly used for graphics cards, however, you can install any PCIe device on them.
This means that you can install not only high-end graphics cards that need the entire x16 bandwidth but also some high-end RAID cards and some faster networking cards that only require a mere X4 bandwidth
Of course, if you install a smaller card on an X16 slot, you will be sacrificing the precious slot that could otherwise be used for graphics card.
Due to their large bandwidth and high scalability, it is best to use a PCIe X16 slot on a machine that has the power and resources to handle it.
This can be great for professional gamers as well as many other professionals in fields such as machine learning where high-speed data processing is required.
Will a PCIe X1, X4 or X8 Card be faster on X16 Slot?
No, the answer is a resounding no. While the X1, X4, or X8 device will certainly FIT physically speaking, it will not gain any type of performance boost.
Here we learned about what does PCIe X16 mean. Basically, whenever PCIe slots or cards are being discussed and you see designations such as X1, X4, X8 or X16, always be confident that these refer to the amount of PCIe lanes or bandwidth of the PCIe slot.
While the above designated can also relate to the physical size, that is NOT always the case since X4 or X8 bandwidth can also be found on slots with X16 physical size.
Nevertheless, the X16 is the largest readily-available size for any PCIe version in the consumer grade market.
Since it offers the highest bandwidth, it is generally used for expansion cards that require highest speeds such as graphic cards.