→ Pci express 4.0 gen4

PCI Express 4.0 is already a reality in our desktop computers thanks to the arrival of the new generation of AMD Ryzen Zen2 and the AMD X570 chipset. The new PCI-SIG standard has been with us since 2017, but it has been in this first half of the year when it has been an option for manufacturers to start giving it the use it deserves. In this article we will see everything we need to know about this new, or better said, updated communication interface.

Index of contents

PCI Express evolution and news

Also known as PCI Express or simply PCI-e, it is a high-speed bus that is used in all desktop and professional computing equipment today. Virtually all high-performance components in a computer send input and output data over such a bus.

The entity under this communication standard is PCI-SIG and unlocked this version 4.0 for the first time in 2017, but it has not reached us, and even our desktops until this year 2019. And the reason is very simple, until now, Very few devices have needed a higher bandwidth than PCIe 3.0 gives us, but with the arrival of the new NVMe solid state storage units, and a higher density of data exchange between CPU and Chipset, this bus has entered from packed in the industry.

Since this standard was implemented in 2003, we have gone through a total of four updates. There has been a constant in all of them, and that is to double the bus width in each iteration. The duration of each of the versions on the market is approximately 4 years, until the arrival of version 3.0, which has been maintained for no less than 7 years until 2017. PCI-SIG has already unlocked even the next update, the PCIe 5.0 in this same quarter of 2019, but on desktops we will remain with this bus for at least three more years, since few are the devices that still need such bandwidth.

Bandwidth

PCI Express is based on lanes, or data lanes, resembling the lane of a highway, but where cars can circulate in both directions, although in this case of electricity. Specifically, PCIe 4.0 is capable of doubling the transfer speed of version 3.0, thus reaching no less than 16 GT / s (Transfer Gigabits) for each of these up and down lanes, due to the fact that it is bidirectional. If we pass this measurement to values ​​with which we work daily, we are facing a speed of 1969.2 MB / s for each lane, compared to 984.6 MB / s for the PCIe 3.0 bus.

Another aspect that also improves is the latency in communications by having a greater bus width and a PHY receiver that manages the information of the electrical margin of each of the lanes thanks to the corresponding PCIe controller. For practical purposes, better bus saturation management and reduced latency in I / O communications are achieved, improving scalability depending on which devices we connect.

As far as need is concerned, PCI Express 4.0 is not yet indispensable today, but a way to prepare for the near future. Network communications at 10 Gbps are becoming more frequent, especially now with the arrival of 5G. The high demand for USB 3.1 Gen2 connectivity and soon USB 3.2 with 20 Gbps, along with the new NVMe PCIe x4 SSDs that already found the limit at 3.94 GB / s, has been one of the main causes of its implementation.

Let's see in the following table a comparison between the different versions of PCIe, as its speed depending on the available configuration:

V.	Introduction	Transfer by lane	Bandwidth
× 1	× 4	× 16
1.0	2003	2.5 GT / s	250 MB / s (2 Gb / s)	1.0 GB / s	4.0 GB / s (32 Gb / s)
2.0	2007	5.0 GT / s	500 MB / s (4 Gb / s)	2.0 GB / s	8.0 GB / s (64 Gb / s)
3.0	2010	8.0 GT / s	984.6 MB / s (7.9 Gb / s)	3.94 GB / s	15.8 GB / s (126 Gb / s)
4.0	2017	16.0 GT / s	1969 MB / s (15.8 Gb / s)	7.88 GB / s	31.5 GB / s (252.1 Gb / s)
5.0	2019	32.0 GT / s	3938 MB / s (31.6 Gb / s)	15.75 GB / s	63.0 GB / s (32 Gb / s)

Backward Compatibility Do we need PCI Express 4.0?

Currently the most famous application that we all know to use the PCIe slots is through the graphics card. At this point we all know that for a self-respecting gaming team we need a dedicated graphics card, which works through PCIe 3.0 x16, that is, we have a 126 Gbps bus to transfer data. But how much do we really need? Well, in a transfer for a game in 4K resolution at 144 Hz and 10-bit color depth, we would need approximately a 35.8 Gbps bus.

This means that we have a bus width of approximately 70% for the transfer of image data. Let's remember that it is bidirectional data, so here the consideration of the upstream and downstream bus already enters. So it definitely doesn't make sense currently to have PCie 4.0 on a graphics card, for example. If we talk about multi GPU, well, the width would be considerably more used due to the parallelism, but still more than enough.

But we can also say that we do need it, and this is due to the incorporation of the new NVMe SSDs. Until now, they all worked using PCI 3.0 x4, but in this aspect, the manufacturers did soon find the limit, reaching read rates very close to those 3.94 GB / s that were available. The solution is not to introduce more lanes in the M.2 slot by simply limiting the capacity of the CPU and chipset, but to increase it to twice the bandwidth, as manufacturers such as AORUS or Corsair, already have their own M.2 PCie 4.0 a more than 4000 MB / s.

So what happens to users who maintain their PCIe 3.0 and want to use a peripheral 4.0? Well, it will not have any problem in terms of connectivity, since from the beginning, PCIe has offered backward compatibility with previous standards. In fact 3.0, 4.0 and soon 5.0 will continue to use 128b / 130b encoding in their transfers. The only drawback will be that it will limit the speed of the bus.

PCI Express 4.0 on SSD and graphics card

The excellent work that has been done on solid storage should certainly be highlighted. Since the M.2 interface appeared working at x4 lanes and under NVMe protocol, the speeds have multiplied in a matter of months, coming to need more than 4000 MB / s for its memory configurations based on 3D NAND.

Manufacturers such as AORUS or Corsair have unveiled their new SSDs capable of working at theoretical speeds of 5000 MB / s in sequential reading and 4400 MB / s in writing with Toshiba's NAND 3D TLC architecture. These figures are approximately 40% more than the previous generation of SSD, and far from having reached the limit, since, although it remains the way to 7 , 88 GB / s available in just 4 lanes.

This change brings some details to consider when installing these SSDs, for example the need to activate the write cache policy to achieve better transfers. Of course, another slightly important detail is having a PCIe compatible board, and for now only AMD will have them.

We recommend checking both options to have the best performance with the SSD

The other device we have on the market with PCI Express 4.0 is the new AMD Radeon RX 5700 and 5700 XT graphics cards. For practical purposes it is not something important, since we have clearly seen that with 3.0 we are left over, but it is not wrong to implement the new standard and lead the way.

AMD Ryzen 3000 and AMD X570, the first compatible with PCI Express 4.0

The first manufacturer to launch into the desktop market with this new PCIe 4.0 has been AMD, thanks to its new generation of Ryzen processors. Some CPUs with lithography in 7 nm FinFET baptized as Zen2 that now offer 16 lanes PCIe 4.0 in its communication interface I / O for graphics card, and a total of 24 lanes. Not only are they processors with a great performance improvement in the handling of instructions, but they are able to work with a much larger volume of data.

In fact, the new motherboards adapted to this new generation use an AMD X570 chipset that has no less than 20 lanes PCI Express 4.0. In an article that we already have prepared, we will see the comparison between X570 vs X470 chipset, etc., and one of the main ones is this. The basic configuration consists of 8 lanes that will be mandatory for PCIe 4.0 and another 8 lanes can be used for other devices such as SATA or peripherals such as USB, for example, with manufacturers having some freedom of allocation. The remaining 4 lanes are of free choice for manufacturers, although in principle they will be intended for a configuration of 4x SATA 6 Gbps or 2x PCIe 4.0 x2.

Thanks to the power of these two elements, the communication bus between CPU and Chipset consists of 4 PCI Express 4.0 lanes. As for slot allocation, we also see quite a few new features compared to the previous generation, since the chipset itself has introduced a few other PCIe x1 and x16 slots (working at x4) 4.0 and even two M.2 x4 slots for these new SSDs. Another substantial change is the support of up to 8 USB 3.1 Gen2 10 Gbps ports, something that until now was not possible.

As for other hardware compatible with PCI Express 4.0, we can mention the IBM POWER9 processor or the Falcon Mesa FPGA with Intel's 10nm manufacturing processor, which is compatible with PCI Express 4.0 as a built-in IP block through EMIB. The new generation of Intel processors is yet to come, and it is clear that it will also implement PCI Express 4.0.

NVME performance difference PCI Express 3.0 vs PCI Express 4.0

Although it is something that we can quickly search through our reviews, we are going to compare the sequential reading and writing of a PCI Express 3.0 SSD against a fourth generation with PCI Express 4.0. The perfect candidates are the Corsair MP510 vs. MP600.

Model	Sequential reading (MB / s)	Sequential write (MB / s)
Corsair MP510	3, 480MB / s	2, 700MB / s
Corsair MP600	4, 950MB / s	4, 250MB / s

And here our tests:

Conclusions and future of the industry

If there is something we must be clear about, it is that for now PCI e 4.0 offers its maximum advantage in terms of storage devices and internal communication between devices, for example, CPU and Chipset. Hardware such as graphics cards, are still far from getting into trouble version 3.0 and much less this 4.0, so for gamers, the result will be practically identical in performance.

PCI-SIG has already unlocked its PCIe 5.0 interface this year, but it is clear that we will not see motherboards with this bus until at least 2022, to try to extend the life of the current standard a little, for today, this 4.0 still It does not have a wide range of applications from each to the ordinary user.

We leave you with the following articles:

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