The motherboard is the hosting platform for the computer host, and it is also the basic device that affects the performance of the entire system. Especially in terms of function expansion, different boards need to be installed, such as graphics cards, professional sound cards, high-performance network cards, RAID disk array cards and other devices, which are all expanded through PCI-E slots. These slots on the motherboard are of different lengths, and many people only recognize the longest graphics card slot when installing a computer. So what is the difference between them?
PCI-E is a common high-speed expansion bus for current motherboards. It is divided into x1, x2, x4, x8, x16, x32 and other specifications, and the corresponding slot lengths are also different. As shown in the picture below, the PCI-E slot is divided into two sections by a fool-proof partition. The section close to the chassis baffle provides basic power supply, reset, clock, device detection, SMBus and other functions. According to the PCI-SIG specification, they physically provide a maximum power supply capacity of 75W. Therefore, the length of this part of all PCI-E specification slots is the same, and there are 22 contact pins inside.
The length of the other section is different depending on the number of channels. Generally speaking, the longer the physical length of the slot, the greater the number of internal contact pins, the more transmission channels provided, and the higher the overall bandwidth. In specifications, they are usually increased by a factor of 2. The following figure shows several common PCI-E slot specifications.
The shortest one is PCI-E The total length of the x1 slot is 25mm. There are only 14 internal data transmission pins (excluding 22 in the power supply part). It can only provide one transmission channel and has limited transmission bandwidth. It is widely used in low-speed peripherals, including independent sound cards, network cards, wireless network cards/Bluetooth and other devices.
The medium-length PCI-E x4 slot has a total length of 39mm. It has 42 internal data transmission pins and can provide 4 transmission channels. It can meet the needs of stable operation of medium-to-high-speed hardware, such as solid-state drives with NVMe protocol, and can also be adapted to advanced peripherals such as 10G network cards and disk array cards. The PCI-E x4 slot also has a special form of slot, the M.2 slot, which is specially used to install high-speed NVMe solid-state drives.
Some people may ask where the PCI-E x2 slot is? In fact, motherboard manufacturers basically do not make dedicated PCI-E x2 physical slots, and some expansion peripheral manufacturers usually reduce the PCI-E x4 specifications. For example, some rare OEM solid-state drives (such as the solid-state drives of XBOX Series X/S game consoles) and microSD Express memory cards have x2 specifications.
Next is the PCI-E x8 slot. Its length is 56mm. It has 76 internal data transmission pins and can provide 8 transmission channels. The transmission bandwidth is four times higher than PCI-E x4, but it can basically only be seen on server motherboards or early consumer motherboards. The PCI-E x8 slots of modern consumer motherboards are often shrunk from the PCI-E x16 slot. We will talk about this in a moment.
Then there is the PCI-E x16 slot, which is the familiar graphics card slot. Its length is 89mm. It has 142 internal data transmission pins and can provide 16 transmission channels. It is also the so-called "full blood" slot. It is usually installed with independent graphics cards.
In addition, the PCI-E x8 slot of the consumer motherboard just mentioned is shrunk from the PCI-E x16 slot. The appearance is no different from the PCI-E x16, but if you look closely, you will find that there are only half the number of data transmission contact pins inside.
In addition, the PCI-E specification also has PCI-E x32 slots with a larger number of channels. The slot length is naturally longer, so it can basically only be seen in servers.
Finally, let’s talk about compatibility. PCI-E is backward compatible. For example, PCI-E x1 devices can be plugged into PCI-E slots of any specifications. To put it bluntly, as long as they can be plugged in, they can be used.
Overall, different PCI-E slots perform their own duties. The short slot is for expansion, the middle slot is for capacity expansion and efficiency, and the long slot is dedicated to core hardware. Proper planning and installation can ensure full hardware performance, and novices can easily avoid misunderstandings about various slots.