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What is the difference between PCIe Gen 3 and PCIe Gen 4?

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Apr 2022

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PCIe has been the standard interface for connecting high-speed peripheral components to computer motherboards for the past decade. The fourth generation of this interface, PCIe 4.0 standard, was announced in 2017. However, we did not see SSDs or graphics cards using the new tech until Computex 2019. Today, PCIe 4.0 has attracted an upsurge of excitement for this technological innovation whether it be SSDs, GPUs, motherboards or high-powered expansion cards. But what is PCIe Gen 4? We’ll break down the basics.

What is PCIe Gen 4?

PCIe Gen 4 is the fourth and latest generation of the PCI Express specification. The successor to PCIe Gen 3, PCIe Gen 4 is the fastest PCIe generation available on the market today.

What does PCIe Gen 4 do?

PCIe Gen 4 allows systems to connect to high-performance PCIe devices such as GPUs and PCIe NVMe SSDs.

Why is PCIe Gen 4 necessary?

Advancement in PCIe technology is necessary to accommodate the growing need for a high-speed data bus that enables increasingly demanding user applications and workloads.

What is the difference between PCIe Gen 3 and PCIe Gen 4?

PCIe Gen 4 doubles the data rate of PCIe Gen 3, allowing PCIe Gen 4 devices to transfer data at much faster speeds. PCIe Gen 3 operates at 8 GT/s (gigatransfers per second) which roughly translates to 1 GB/s per PCIe lane. By comparison, PCIe Gen 4 operates at 16 GT/s, or around 2 GB/s (gigabytes per second) per PCIe lane.

What is the maximum bandwidth of PCIe Gen 4?

To understand the maximum bandwidth of a PCIe Gen 4 device, you must know the number of PCIe lanes that it supports. PCIe devices use “lanes” for transmitting and receiving data, so the more lanes a PCIe device can use, the greater the bandwidth can be. The number of lanes that a PCIe device supports is typically expressed like “x4” for 4 lanes, “x8” for 8 lanes, and so on.

	x1	x2	x4	x8	x16
PCIe Gen 3 bandwidth	1 GB/s	2 GB/s	4 GB/s	8 GB/s	16 GB/s
PCIe Gen 4 bandwidth	2 GB/s	4 GB/s	8 GB/s	16 GB/s	32 GB/s

Is PCIe Gen 4 backward compatible?

PCIe Gen 4 is backward compatible, so a PCIe Gen 4 device connected to a PCIe Gen 3 system will function normally at PCIe Gen 3 speeds. That means if you purchase a PCIe Gen 4 NVMe SSD today, you can use it immediately in your current system even if it does not support PCIe Gen 4. If you upgrade to a PCIe Gen 4 system in the future, you will unlock the full performance of your PCIe Gen 4 NVMe SSD.

When will PCIe Gen 4 become available?

PCIe Gen 4 is currently under industry adoption and many PCIe Gen 4 products are available on the market today. However, only the latest products will support PCIe Gen 4. Moving forward, PCIe Gen 4 will become the industry standard.

How do I get PCIe Gen 4?

To take advantage of PCIe Gen 4, your CPU, motherboard, and PCIe devices must all support PCIe Gen 4.

What desktop platforms currently support PCIe Gen 4?

Some desktop CPUs and motherboards which support PCIe Gen 4 and are currently shipping include:

AMD Ryzen™ 3000 and 5000 series CPUs
AMD X570, B550, and TRX40 motherboards
Intel® 11th Gen «Rocket Lake» and 12th Gen “Alder Lake” Core CPUs
Intel® Z490, Z590, and Z690 motherboards

What is a PCIe NVMe SSD?

PCIe NVMe SSDs are solid state drives that use the high-speed PCIe bus for data transfer as well as the NVMe (Non-Volatile Memory Express) protocol to communicate with the host system. As these drives operate on the PCIe bus, they offer vastly improved bandwidth and quicker response times than SATA SSDs.

Does PCIe Gen 4 make PCIe NVMe SSDs faster?

PCIe Gen 3 was unable to accommodate the full bandwidth of high-speed PCIe NVMe SSDs. This was effectively creating a bottleneck in SSD performance. PCIe Gen 4 solves this performance bottleneck, allowing PCIe NVMe SSDs to read and write data at much faster speeds.

What form factors are used by PCIe NVMe SSDs?

PCIe NVMe SSDs can use various form factors such as add-in card (AIC), M.2, and U.2. Client PCIe NVMe SSDs typically only use the M.2 2280 form factor because its slim design allows it to easily fit into desktop and notebook PCs. Enterprise-class PCIe NVMe SSDs will use all three form factors, with U.2 being the most popular because of its compatibility with server backplanes.

Conclusion

PCIe 4.0 platforms allow for more flexibility and available bandwidth. SSDs that utilize a PCIe 4. 0 interface are ideal for data-intensive workloads. They load applications and games faster while also optimizing boot load up time. PCIe 4.0 also brings power-saving enhancements, meaning your device runs cooler while consuming less power. With the emergence of more products adopting PCIe 4.0, the decision between PCIe 3.0 and 4.0 is a no-brainer. PCIe 4.0 will be an industry standard before you know it.

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Definition > PCI Express — PCI-Express

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PCI (Peripheral Component Interconnect) Express is a bus extension standard that appeared in personal computers in 2004. Its purpose is first of all to replace the AGP bus, then the PCI bus on all motherboards. The allocated speeds vary between 312 MB/s and 10 GB/s, compared with 133 MB/s maximum for PCI and 2 GB/s maximum for AGP (Accelerated Graphics Port).

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What is PCI Express ?

PCI Express is a bus that is used to connect a variety of components to a desktop PC. With its help, video cards, network cards, sound cards, SSD drives, WiFi modules and other similar devices are connected. The development of this bus was started by Intel in 2002. Now the non-profit organization PCI Special Interest Group is developing new versions of this bus.

At the moment, the PCI Express bus has completely replaced such obsolete buses as AGP, PCI and PCI-X. The PCI Express bus is located at the bottom of the motherboard in a horizontal position. nine0003

What is the difference between PCI Express and PCI

PCI Express is a bus that was developed from the PCI bus. The main differences between PCI Express and PCI lie at the physical level. While PCI uses a common bus, PCI Express uses a star topology. Each PCI Express device is connected to a common switch with a separate connection.

The PCI Express software model is largely the same as the PCI model. Therefore, most existing CI controllers can be easily modified to use the PCI Express bus. nine0003

In addition, the PCI Express bus supports new features such as:

Device hot plugging;
Guaranteed data rate;
Energy management;
Integrity control of transmitted information;

How the PCI Express bus works

The PCI Express bus uses a bidirectional serial connection to connect devices. Moreover, such a connection can have one (x1) or several (x2, x4, x8, x12, x16 and x32) separate lines. The more such lines are used, the more data transfer speed the PCI Express bus can provide. Depending on the number of lines supported, the sort size on the motherboard will differ. There are slots with one (x1), four (x4) and sixteen (x16) lines. nine0003

Visual demonstration of PCI Express and PCI slot sizes

Any PCI Express device can work in any slot if the slot has the same or more lanes. This allows you to install a PCI Express card with a x1 slot in a x16 slot on the motherboard.

PCI Express throughput depends on the number of lanes and bus version.

One/two way Gbps
	Number of lines
	x1	x2	x4	x8	x12	x16	x32
PCIe 1.0	2/4	4/8	8/16	16/32	24/48	32/64	64/128
PCIe 2.0	4/8	8/16	16/32	32/64	48/96	64/128	128/256
PCIe 3.0	8/16	16/32	32/64	64/128	96/192	128/256	256/512
PCIe 4. 0	16/32	32/64	64/128	128/256	192/384	256/512	512/1024

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What is PCIe? Parsing | Droider.ru

We all hear about PCI-Express lines all the time. There are 8 of them here, there are 16 of them. Here is PCI-Express 3.0, here 4.0, etc. But what does it all mean? And why is it now almost as important to have a fresh PCI Express as a powerful processor or video card?

Therefore, today we will understand the technology? Let’s find out what a tire is.

Compare gigatransactions and gigabytes. And also find out why PCI Express is the fastest way to get you to work. nine0003

What is it?

First, let’s figure out what is PCI-Express and why is it needed?

And for this, let’s solve a logic problem.

Here is a 4K monitor, a powerful graphics card and a fast SSD drive. What do all these devices have in common? In addition, all this now costs incredible money.

Let’s reason. All these devices for normal operation need to exchange data with the central processor, and in huge volumes and at high speeds. Therefore, all these devices can be connected to the CPU via the high-speed PCI-Express bus. nine0003

PCI Express (Peripheral Component Interconnect Express)

What is a bus and why is it high speed?

Well, look, in order to combine something with something inside the computer, we firstly need a physical connection, and secondly, some kind of protocol, that is, the rules by which data will be transmitted.

So that’s both in one bottle — this is the tire. And PCI-Express is one of the fastest buses. But how fast?

Here I have a laptop, this is MSI GP66 Leopard 11UH-229RU. It supports the current PCIe version 4.0.

Theoretically, if you put a fast SSD with PCIe Gen 4 support here, you can get speed 7, maybe even 7.5 GB / s. Imagine 7 GB per second! And I have seen such figures in practice!

And since there is a slot for a second disk, if you combine two disks in a RAID, you can double this figure.

But in my configuration, not the fastest Kingston SSD with QLC memory and only PCIe 3.0 support is installed. Therefore, it will not be possible to test the bus’s capabilities on it. nine0003

But where do these speeds come from? What are these lines? And what PCIe is really capable of, let’s talk about this.

How does PCIe work?

So why is PCIe so fast. First of all, it’s about architecture.

Imagine that you need to drive from your home to your office, which is 10 km away from you. Under what conditions will the journey take the least time? It should be straight, with no speed limit, and preferably no other cars at all.

So, just PCI (without express) worked like a regular city road network, all devices were connected in parallel to a common bus, that is, their data ran along the same roads. Therefore, the speed of work could vary depending on the traffic.

But the PCIe standard has paved an individual path for each device, which directly connects it to the central hub, located either on the same chip with the central processor, or separately on the chipset. Therefore, PCIe guarantees a stable maximum connection speed for each device. nine0003

Moreover, such an individual road is two-way. Therefore, data can be transferred in one direction and the other at the same time at full speed. This mode of data transmission is called duplex.

Each such path from the device to the switch is called a PCIe lane. And there are several such lines to each device: 1, 2, 4, 8 or 16, depending on the needs. Therefore, the more lines, the greater the speed, that is, 2 lines are 2 times faster than one, and 16 lines are 16 times faster. And no loss. nine0003

I think that the general principle is clear, but now let’s go a little deeper and figure out exactly how data is transmitted.

Gigatransactions

The speed is affected not only by the architecture, but also by the method of data transfer.

At the electrical level, each connection uses low-voltage differential signaling, or LVDS — low-voltage differential signaling.

We will not delve into this much. But in general terms, in LVDS, the signal is encoded by applying different voltage levels with a very small signal amplitude. nine0003

This approach avoids interference in the outside and transmits data at high frequencies using a cheap copper twisted pair. In general, the benefits are many.

Computer buses transmit data in packets. Each packet of transmitted data is called a transaction. Therefore, the data transfer rate in buses is measured not in gigabits or gigabytes per second, but in gigatransactions per second (well, or gigatransfers, they also say so). What it is?

In fact, a transaction per second is not the amount of data transferred, but the frequency with which this data is transferred. And the higher this frequency, the higher the throughput. nine0003

It looks like a CPU, the more gigahertz, the theoretically faster.

For example, in PCI-e 1.0, each line operates at a frequency of 2.5 GT / s, that is, 2.5 billion transactions per second. And in version 2.0. the frequency is 2 times higher than 5 GT / s, therefore, the interface bandwidth is 2 times higher.

One lane of PCIe 1.0 transferred 0.25 GB/s, and 2.0 was already 0.5 GB/s.

But not only the bus frequency affects the throughput.

In PCIe 3.0, the frequency has grown from 5 GT / s to 8, and it seems that this is not much. But at the same time, the throughput has almost doubled! How so? nine0003

The fact is that the speed of the bus is also affected by the method of encoding information.

When transferring data, it is important for us to be sure that everything has arrived safe and sound. Therefore, special integrity check codes and other service information are added to each data packet, which also take up space.

For example, in the first and second versions of PCIe, there were 2 service bits for every 8 bits of useful information. This encoding is denoted as 8 bits divided by 10 bits. or 8b/10b. nine0003

This means that 20% of the bus bandwidth was spent on the transfer of service information.

Starting with the 3rd version of the interface, they began to use 128b/130b encoding. This means that for every 2 bits of service information, there are 128 bits of useful information. And this is only 1.5% loss. Therefore, despite the slightly increased frequencies from 5 to 8 Gigatransfers, in the third version of PCIe, the bandwidth increased by almost 2 times.

By the way, if you want to accurately calculate the throughput of each PCIe version, you can do it with this formula. Well, or just look at the plate on Wikipedia. nine0003

PCIe bandwidth formula:

BW (MB/s) = FR (MT/s) * EN * 1B/8b
BW — desired transfer rate in MB/s
FR — bus frequency in GT/s
EN — coding type
Example, for PCIe 2. 0:
BW = 5000 * 8/10 * 1/8 = 5000 * 0.8 * 0.125
BW = 500 MB/s

Why do I need PCIe 4.0?

The current version is PCI Express 4.0. Unlike the previous version 3.0, the new bus is 2 times faster, the data transfer rate on the bus here reaches 16 billion transfers per second. And the throughput of one line here reaches almost 2 GB / s (1969 MB/s). And as much as 31.5 GB / s for 16 lines!

Just imagine — 31 GB per second!!! But why is this needed and how does it affect performance in general?

Well, look, the 3rd generation of the tire appeared already in 2010 and is still used almost everywhere. And the 4th generation was ready back in 2017, but only now it is starting to become mainstream.

Everything is developing so slowly because up to now there have been very few tasks for which such data transfer rates would be needed. That is, there was no point in updating before. nine0003

But now there are affordable and super fast SSD drives that are not enough for the standard 4x PCI 3. 0 lanes at 3.9 GB / s. And then there are powerful graphics cards and high-resolution monitors that also need a lot of bandwidth.

Therefore, first of all, PCI-e 4.0 is needed for modern games and support for DirectStorage technology from Microsoft.

If you want games to load fast, textures to load quickly and be in high photorealistic resolution, and level transitions and location changes to be seamless, a fast SSD and PCIe 4.0 is a must. nine0003

All of these things are already standard on next generation consoles, and so all future games will also be developed with these new fast streaming capabilities in mind.

Secondly, if you have several 4K and 5K monitors that you work with at the same time, the presence of PCI Express version 4 may also become a necessity. But these are already more professional cases, and here people themselves know what they need.

How does it affect performance?

Okay, let’s move on to practice and our test laptop MSI GP66 Leopard

MSI GP66 Leopard 11UH-229RU

Intel Core i7-11800H
RAM 16 (2×8) GB DDR4-3200
Nvidia GeForce RTX 3080 video subsystem
Screen 15. 6, 1920×1080, 144Hz, IPS
SSD 512 GB + free M.2 slot 2280
Battery 65 Wh
Dimensions 358×271×34 mm (maximum, measured by us)
Weight without power supply 2.32 kg (measured by us)

This laptop’s strengths include a powerful 11th gen Intel 11800H processor, which has 20 PCIe 4.0 lanes to better expose the Nvidia RTX 3080 graphics card. IPS display from LG with a refresh rate of 144Hz.

Well, the main drawback is the bundled SSD, which clearly does not reveal the capabilities of hardware. However, you can always add a second SSD if that’s not enough. nine0003

This laptop is not marketed as a gaming laptop, but rather a computing laptop. But judging by the characteristics, as well as the RGB backlighting of the keyboard. We seem to understand exactly what calculations you mean by MSI, so we ran Cyberpunk 2077 on it.

And the laptop performed great in the gaming test. In Cyberpunk 2077, I set the settings to ultra and in the laptop to the extreme performance mode.

Also see test results in other games in comparison with competitors:

(Source ixbt.com)

It is difficult to say how much the presence of PCI Express 4.0 affected these results. But the interface was definitely not a bottleneck, and its full potential may be revealed in the future, when support for DirectStorage technology appears in Windows and if you install a new SSD.

Otherwise, the laptop is very good for demanding computing and just perfect for gaming.

What to expect in the future?

What can we expect in the future? We are waiting for PCI Express 5.0 and 6.0, each of which is twice as fast as its predecessor.

The 5th generation specification was finalized back in 2019, and the first processors to support the new bus will be available very soon in November 2021, these will be Intel 12th generation Alder Lake processors.

No need for 5th tire generation speeds yet. Almost everyone will have enough of the 4th version for many more years.