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Hardware Guide: What is PCIe 4.0 and why is it important for PC gaming?
By Jon Sutton on June 23rd, 2019 at 04:00pm - original article from game-debate

PCI Express 3.0 has been the standard for eight long years. For this duration, outside of the restrictions placed by not being able to upgrade, it’s largely been something we just haven’t had to think about.

That’s all set to change over the next five or so years though, PCI Express 4.0 is about to go mainstream in a matter of weeks with the arrival of the Ryzen 3000 series and the assorted X570 chipsets. On top of this, the PCIe 5.0 specs were finalised, while PCIe 6.0 was just announced. After eight years of stagnation, we’re about to get some significant change.

PCI Express 6.0

What is PCI Express?

But what does it all mean? Well, let’s start with what PCI Express is, and also what it does. PCI Express (Peripheral Component Interconnect Express) is a serial computer expansion bus standard. To you and I, it’s the slots we use to put in our dedicated graphics cards, or our M.2 SSDs if you’re feeling flush. They’ve got a variety of other different uses as well, including wireless network cards, ethernet connections, RAID cards, and sound cards. PCIe is, to put it bluntly, rather important. It’s the system through which a number of key hardware components will interface with your motherboard.

Since the first PCIe internet connect standard came to market (PCIe 1.0), the effective bandwidth has doubled with each generation. Start at 8GB/s to in 2004, rising to 16GB/s with PCIe 2.0 in 2008, and landing at 32GB/s with PCIe 3.0 in 2011. And that’s where we’ve been stuck for eight years. PCIe 4.0 is becoming broadly available right now though, with 64GB/s effective bandwidth, rising to 128GB/s and 256 GB/s with PCIe 5.0 and PCIe 6.0 respectively.

PCI Express Bandwidth Speeds

Aside from the version number, you’ve probably also seen the likes of PCIe x4, PCIe x16, etc. This refers to the number of data lanes on any given PCIe connection and, physically, means a 16x connection is longer than a 1x port, for example.

PCIe GuideFor the most part, you’ll only see PCIe x1 through to PCIe x16 in consumer products. PCIe x32 does exist, with 32 data lanes, but these are rare. The greater the number of data lanes, the greater the bandwidth possible between the component and the motherboard.

However, between the various generations of PCI Express, the physical size has remained exactly the same. This means an x16 GPU which launched in 2004 will slot into an x16 PCIe 6.0 slot in 2022 just fine.

For the end user, your concern should be in making sure you have enough data lanes to provide sufficient headroom for the component you’re putting in. Most graphics cards should always go in a PCIe x16 slot, for example. Any fewer lanes and the graphics card will be throttled. There are a few x8 graphics cards out there, but they can go in an x8 or x16 PCIe slot without loss of performance. Likewise, an x1 sound card could go in an x16 slot without issue.

Will PCIe 4.0 improve my graphics card performance?

From a pure numbers standpoint, PCIe 4.0 will be twice as fast as the PCIe 3.0. Bandwidth jumps from 32 GB/s flowing in each direction up to 64 GB/s, while frequency increases from 8 GHz up to 16 GHz. This doesn’t mean that any hardware you put in a PCIe 4.0 slot will just run twice as fast though.  

You’ll see much higher bandwidth than 32GB/s advertised with graphics cards, of course but this is actually the speed at which the GPU interfaces with the onboard VRAM rather than with the rest of the system.

As it currently stands, graphics cards don’t even use the full bandwidth capacity of PCIe 3.0. An RTX 2080 Ti at 4K won’t be fully saturating a PCIe 3.0 x16 interface. Drop an RTX 2080 Ti into a PCIe x4 slot and it’ll barely make a dent into performance.

PCI Express 4.0 scaling performance gaming

In order for a graphics card to actually benefit from PCIe 4.0, demos are using 8K @ 120Hz. That’s the sort of level where PCIe 4.0 could become beneficial from a gaming perspective.

So why should I be interested in PCI Express 4.0 and beyond?

The key beneficiary to PCIe 4.0 will be, first and foremost, storage. All those NVMe M.2 SSDs which are all the rage these days will benefit from lighting fast transfer speeds. The solid-state drives plug straight into an NVMe slot on your motherboard, rather than a SATA connection, providing sequel read and write speeds that are many times faster. A typical SSD using a SATA drop can peak at around 550MB read and write, while first-generation PCIe 4.0 M.2 SSDs are already reaching read and write speeds of 5GB/s.

In gaming terms, this means lightning quick loading speeds and the ability to pull assets from the SSD faster during gameplay. This means you could travel faster without the game hitching, for example.

Outside of games, OS boot times should be pretty ludicrous. It’s already nice and nippy with a standard SSD, but an M.2 NVMe drive utilising PCIe 4.0 should boot in but a few moments.

But, the key beneficiaries of PCIe 4.0, 5.0, and beyond, will largely be data centres rather than individual users. Cloud computing, for example, benefits from data centres filled with high-speed, high-core CPUs, fast GPUs, high-performance storage, and minimal latency. Next-gen PCI Express will help with all of this, and data centers are likely to ramp up the usage of PCIe 4.0 very quickly. They’re dealing with vastly computing power than we are at home, and it’s here we can expect to see the more obvious benefits right now.