Pci express x16, x8, x4 and x1 connectors: differences and performance

In this article we are going to see the differences between the PCI Express x1, x4, x8 and x16 modes, as well as check if there is any difference in the performance of a current graphics card. Is there such a difference between their speeds?

Index of contents

PCI Express x1, x4, x8 and x16

Peripheral Component Interconnect Express (PCI Express), officially abbreviated as PCIe, is a high-speed serial computer expansion bus standard designed to replace older PCI, PCI-X, and AGP bus standards. The PCI Express electrical interface is also used in a variety of other standards, especially in ExpressCard as a notebook expansion card interface, and in SATA Express as a storage interface.

We recommend reading our article on PCI Express which is

In PCI Express x1, x indicates the physical size of the PCIe card or slot, with x16 being the largest and x1 being the smallest. The PCI Express interface enables high-bandwidth communication between the device and the motherboard, as well as other hardware. The more data channels are connected, the greater the bandwidth between the card and the host. However, there is generally a cost increase that is incurred with a greater number of lanes.

PCIe is an updated version of the PCI protocol. Similar to PCI / PCI-X interfaces, PCIe was developed for interfacing peripheral components. PCIe differs from PCI / PCI-X in several ways. However, a key difference will allow us to better understand the differences between the variations of the PCIe protocol (x1, x4, x8, x16 and x32). That key difference is "parallel" data transmission versus "serial" transmission. In the PCI and PCI-X architecture, all cards share parallel data lines to and from the host. Differences between card speeds and slot types lead to limited data speeds.

PCI Express is organized in lanes. Each lane has an independent set of transmit and receive pins, and data can be sent in both directions simultaneously. And this is where things get tricky. The one-way bandwidth for a single PCIe 1.0 (x1) lane is 250MB / s, but because it can send and receive 250MB / s at the same time, Intel likes to indicate the available bandwidth for a PCIe 1.0 x1 slot as 500 MB / s. While that's the total aggregate bandwidth available for a single slot, you can only reach that bandwidth figure if you're reading and writing at the same time.

• 'PCIe x1' connections have one data lane 'PCIe x4' connections have four data lanes 'PCIe x8' connections have eight data lanes 'PCIe x16' connections have sixteen data lanes 'PCIe x32' connections have thirty-two data lanes (currently very rare)

This allows each card connection to achieve independent bandwidth from other cards that may be active in the system. The number of lanes is indicated by the PCIe protocol suffix (× 1, × 4, × 8, × 16, × 32). Each lane is capable of speeds of 250-1969 MB / s, depending on the version of the PCIe protocol (v1.x, v2.x, v3.0, v4.0). PCIe cards can always operate in PCIe slots with the same or more lines than the card. For example, an x8 card can operate in a slot with x8, x16, or x32 lanes. Similarly, an x1 card can operate in any PCIe slot.

Does it affect performance?

As we have mentioned, the number of lanes affects the bandwidth of the PCIe interface, something that can negatively affect the performance of connected devices if the bandwidth is insufficient. The following table details the bandwidth of all versions of PCIe.

WE RECOMMEND YOU Is it worth cooling the graphics card by water?

	PCI-e 1.0	PCI-e 2.x	PCI-e 3.0	PCI-e 4.x
x1	250MB / s	500MB / s	985MB / s	1969MB / s
x4	1000MB / s	2000MB / s	3940MB / s	7876MB / s
x8	2000MB / s	4000MB / s	7880MB / s	15752MB / s
x16	4000MB / s	8000MB / s	15760MB / s	31504MB / s

Generally, PCs offer 24 PCIe lanes for graphics cards, which means that if we mount two of these, one of them must work in x16 mode and the other in x8 mode. Gamernexus has done a series of tests to see if there are differences between using a graphics card in x16 and in x8. The testing environment was as follows:

GPU	MSI GTX 1080 Gaming X
CPU	Intel i7-5930K CPU
Memory	Corsair Dominator 32GB 3200MHz
Motherboard	EVGA X99 Classified
PSU	NZXT 1200W HALE90 V2
SSD	HyperX Savage SSD
Box	Top Deck Tech Station
Heatsink	NZXT Kraken X41 CLC

Without further delay we turn to see the results obtained by Gamernexus:

MSI GTX 1080 Gaming X	PCIe X16	PCIe X8
Metro: Last Light	96 FPS	95 FPS
Shadow of Mordor	108 FPS	107 FPS
Call of Duty: Black Ops 3	140 FPS	140 FPS
GTA V	58.3 FPS	58 FPS

Final words and conclusion about PCI Express x1, x4, x8 and x16

As we have seen, there is no performance difference between using a graphics card in PCIe X8 mode and using it in PCIe x8. The results of Gamernexus speak for themselves, and at most we see a difference of 1 FPS, something that is not at all significant and that may be due to a multitude of factors as one more object on the screen at that particular moment.

We also recommend reading:

With this it can be said that PCIe x8 offers enough bandwidth for current graphics cards, it will be interesting to see if it continues to be so in the future.

Gamernexus font