Preface
Gamers who follow us or who are frequent on desktops should be familiar with the term PCIe, which is often found on motherboards, graphics cards, and even hard drives. It can be said that it is one of the most important interfaces or channels in your computer, but it seems that many people do not know what it is, what it can do, and think that it can only be used to insert graphics cards, but in fact it is very versatile, today let's take a brief look at this mysterious "PCIe".
What is a PCIe slot?
PCIe is a high-speed bus of a computer, and the bus is equivalent to a road in the computer, providing data interaction between different devices and hardware. The earliest PCIe was proposed by Intel in 2001, and even then it was not called "PCIe", but "3GIO", which was used to replace the old buses such as PCI, PCI-X, and AGP.
You may not understand this yet, so let's find a motherboard and take a look, the circled place in the picture is what we call the PCIe slot.
What is PCIe used for?
The PCIe interface is often used to connect high-performance peripherals to your computer. The most common example is your graphics card (GPU), as modern gaming, science, engineering, and machine learning applications involve processing large amounts of data. PCIe is a good bridge between the CPU and the GPU, allowing them to interact with each other.
However, graphics cards are not the only devices that can access PCIe slots, and there are many peripherals that can also use PCIe slots, which we will explain to you in detail below. It is worth mentioning that PCIe is not set in stone, it will also be upgraded and iterative, after all, the original version was already in 2001, and now it is 3202, and PCIe has already gone through several iterations.
The history of the PCIe era
Up to now, there are multiple generations of standards for PCIe slots, and the most advanced PCIe 6.0 specification has been released on January 22, 2022, but it is only in the theoretical stage, and no products have been applied or tested.
Don't look at PCIe is now glorious, its predecessor is actually ISA, in that computer is not standardized, various hardware interfaces, protocols are not unified in the era, the hardware on the computer is due to the dispute between the six countries, my hardware is not compatible with yours, your hardware does not support mine, in order to solve this situation, at that time the industry unified a specification, that is, ISA interface, can be regarded as the grandfather of PCIe, it was first born in 1981, carried on IBM computers, and once dominated the PC field at that time.
However, the good times did not last long, as the first generation of data bus, only 8MB/s transfer rate, in today's view, the U disk is faster than it. As a result, the ISA's transmission rate soon could not meet the needs of other hardware, and the interface had problems such as high CPU usage at that time, so everyone began to look for a successor to the ISA.
So PCI was born, PCI compared with ISA in the bandwidth rate has been greatly improved, 32bit width can achieve 128MB/s, if the data bit width is upgraded to 64 bits, the rate can also be doubled to 256MB/s. And it's plug-and-play, just like we plug in the host computer now, and the system can automatically look for the corresponding driver. You must know that in the era of ISA, we needed to manually configure the ISA interface when accessing any device, which was quite troublesome. However, the PCI bus is not without its shortcomings, one is that it adopts a shared bus design, so multiple devices are easy to cause bandwidth grabbing, and secondly, it does not support hot swapping.
And our protagonist PCIe today is evolved on the basis of PCI, and the e on the PCIe suffix is also called Express, which is an upgraded version of PCI at a glance. It differs from PCI mainly in different bus types, different colors, different specifications, and different transmission rates.
At present, the PCIe specification has developed 6 major versions, and each major version evolution can bring nearly double the bandwidth compared to the previous version. The first official PCIe specification, PCIe 1.0, was born in 2003, with a signal rate of 2.5GT/s, 8b/10b encoding, and a single-lane unidirectional bandwidth of 250MB/s and a 16-lane bidirectional bandwidth of 8GB/s. The specification was followed by PCIe 1.0a and PCIe 1.1 versions, which were improved in detail but the bandwidth remained the same.
The PCIe 2.0 specification was officially released in 2007, and the biggest change from the PCIe 1.0 specification is that the signal rate is doubled to 5GT/s, so its bandwidth has also doubled, with a unidirectional bandwidth of 500MB/s for a single lane and 16GB/s for a 16-lane bidirectional bandwidth. In addition, the PCIe 2.0 specification also doubles the power supply capacity of the corresponding slot to a maximum of 150W, but due to various considerations such as compatibility and motherboard power supply pressure, in the end, whether it is a motherboard manufacturer, a graphics card manufacturer, or other PCIe equipment manufacturers, in product development, they are in accordance with the power supply requirements of the PCIe 1.0 specification, that is, 75W, and those with power supply requirements higher than 75W are all equipped with external power supply, which has been used to this day.
Although PCIe 3.0 is a standard released in 2010, it is still used by many devices, compared with the PCIe 2.0 specification, not only the signal rate has been increased to 8GT/s, but also the encoding method has been changed to a more efficient 128b/130b mode, so the single-channel unidirectional bandwidth has been nearly doubled, reaching the level of 985MB/s, and the 16-channel bidirectional bandwidth is up to 32GB/s.
PCIe 4.0 can be considered the current mainstream standard, once again doubling the signal rate, reaching the level of 64GB/s for 16 lanes in both directions, PCIe 4.0 will allow faster transfer of data being loaded in GPU memory and reduce latency on the PCIe bus. As file sizes and graphics complexity continue to increase in video games, and machine learning applications continue to require larger and larger data sets, PCIe 4.0 will play an important role in increasing frame rates and reducing compute time.
PCIe 5.0 was proposed as early as 2019, but it wasn't until last year that AMD's X670, B650 and other motherboards hit the market, that it was really applied to hardware, and now there are gradually PCIe 5.0 SSDs appearing, and players can see the performance of PCIe 5.0. One of the most important features of PCIe 5.0 – and one that everyone will care about – is speed. PCIe 5.0 is twice as fast as PCIe 4.0, with up to approximately 64GB/s unidirectional bandwidth and 128GB/s bidirectional bandwidth.
It is worth mentioning that in data transmission, PCIe 5.0 also uses the NRZ 128b/130b encoding technology imported from the 3.0 standard era, no longer using the 8bit/10bit small packet verification method, but using the new algorithm of 128bit/130bit large packet verification method and a new hardware scrambling and decoding module, etc., its verification bandwidth overhead is reduced from the previous 20% to 1.54%. Even after deducting the lost bandwidth, the PCIe 5.0 x16 and PCIe 5.0 x4 interfaces can provide 63.0 GB/s and 15.75 GB/s of transmission bandwidth, respectively.
PCIe 6.0 is a standard that was only proposed in 2022 and is newly released. The transfer speed is twice that of PCIe 5.0, with a bandwidth of up to about 128GB/s in one direction and up to 256GB/s in both directions. Compared with PCIe 5.0, PCIe 6.0 enhances transmission bandwidth and energy efficiency, while providing low latency and reduced bandwidth consumption.
As for version 7.0 of the PCIe specification, in June this year, the PCI-SIG finalized the draft of PCIe Gen7 (PCIe 7.0) v0.3, which will double its data transfer rate again to about 256GB/s unidirectional bandwidth and up to 512GB/s bidirectional bandwidth. However, there is one thing to say, home PCs should not be able to use such speeds for many years, and the popularity of PCIe 7.0, it is not even known that it will be until the Year of the Monkey, after all, 5.0 has not yet been popularized.
Why does PCIe come in different lengths?
The bus bandwidth of the PCIe interface is PCIe X1, PCIe X2, PCIe X4, PCIe X8, PCIe X16 by length. Although it is possible to plug any length of PCIe devices into the PCIe X1 or PCIe X16 slots, this obviously creates a problem, as devices with small bandwidth requirements will waste the huge bandwidth of PCIe X16, and devices with large bandwidth requirements will "not have enough" in the PCIe X1 slot.
Of course, some gamers may say "I don't have a PCIe X1 slot on my motherboard", in fact, this is normal, on some MATX, ITX and even flagship motherboards, due to the space layout problem, there is no way to plug the PCIe X1 slot, so if you want to use PCIe X1 peripherals, in the absence of a PCIe X1 slot, you can also install a smaller expansion card in a larger slot, which will still work very well.
In general, the purpose of PCIe differentiation is to allow various devices to operate at the appropriate bandwidth, and the bandwidth that different lengths of slots can withstand is different, and the bandwidth that different versions of PCIe of the same length can withstand are also different. Let's take a look at how much difference the bandwidth of different slots can be under each version of PCIe.
As you can see from the graph, PCIe X1 is the slower, PCIe X2 is 2 times faster than X1, X4 is 2 times faster than X2, and so on X16 is 2 times faster than X8. Each iteration of the PCIe version also improves on the speed of the previous generation, and almost every generation is twice as fast as the previous generation. Moreover, PCIe is backward compatible, PCIe 1.0 devices can be plugged into the 2.0 interface, and 2.0 devices can also be plugged into the 1.0 interface, but they can't play their full performance.
What else can be plugged in besides a graphics card?
As we mentioned above, PCIe slots have different lengths, and graphics cards are often plugged into PCIe X16 slots, so what can be plugged in other than plugging in graphics cards? Of course, PCIe X16 slots will also be used to connect RAID array cards, because of its direct connection with the CPU, and the physical distance is closer to the CPU, so the graphics card or RAID array card will have lower latency and better performance when interacting with the CPU.
Most PCIe x8 slots are also PCIe x16 slots on motherboards, but only half of the data pins are active, which means that the actual bandwidth is only half that of a real PCIex16 slot. Mainly used to connect M.2 NVME expansion card, after all, in the past, the motherboard's M.2 interface was not as much as the current motherboard, and the solid-state price at that time was not as low as today, everyone bought a hard disk to save money, only to use 500G, and even before 1T was a rich brother could afford to use the equipment. Therefore, if you want to install more M.2 solid-state on the old motherboard, you need to use this expansion card, and as long as the protocol version and number of channels are the same as the hard disk, the theoretical speed is no different from the onboard M.2.
Like the PCIe X8 slot, the PCIe X4 slot is now mostly made into a PCIe x16 slot or expanded to an M.2 port for installing M.2 SSDs, M.2 wireless network cards or other M.2 interface devices.
Finally, there is the most versatile PCIe X1 slot, which is a short and compact slot, you can buy almost all the interfaces you want to use on the Internet for expansion and adaptation, such as installing USB 2.0/3.0 expansion cards, installing Gigabit/2.5Gbps high-speed network cards, installing high-performance sound cards, expanding more SATA ports, installing Wi-Fi network cards, and so on.
In addition to the slot form, PCIe can also exist in the form of a channel, our most commonly used M.2 SSD interface, on the surface, M.2 connects our SSD, but it is the PCIe lane that plays a role in data transmission. To put it simply, the M.2 interface is a PCIe interface with a different form factor. You see if its interface is very much like a reduced PCIe interface, which is why we can always hear about PCIe 4.0 SSDs and PCIe 5.0 SSDs.
epilogue
While PCIe 3.0 and PCIe 4.0 are still being used in mainstream applications, we are seeing the adoption of PCIe 5.0 in some data centers, as well as new GPUs, CPUs, or SSDs. In the future, the emergence of PCIe 6.0 and even PCIe 7.0 is bound to allow more hardware to release stronger performance. However, according to the current situation, PCIe 5.0 is more like a product of the future, although we also said that there are solid-state drives that support PCIe 5.0 and even graphics cards that support PCIe 5.0, but even PCIe 3.0 will not make the performance of the current graphics card a bottleneck. The emergence of PCIe 5.0 is more like having an ecological foundation, paving the way for future hardware, and also so that the current hardware can adapt to the suddenly explosive AIGC field, after all, the current AI computing model is unimaginably large.