PCIe 2.0 vs 3.0: How Do They Differ?

Mehak Sohail | Last Updated On November 22nd, 2021

As you’re looking to upgrade your PC, you may have been confused about PCIe and all the different versions. Beginner PC builders can have trouble making sense of all the confusing annotations and numbers.

For this reason, I’ll explain precisely what PCIe slots are and help you make the most out of your computer in this in-depth guide. If you want to know what can be plugged into PCIe Slots, read here.

The main difference between PCIe 2.0 and 3.0 is that the newer 3.0 version has doubled the available bandwidth of the predecessor. More specifically, PCIe 3.0 offers 0.985 GB/s per PCIe lane, and PCIe 2.0 provides a bandwidth of 0.50 GB/s per PCIe lane. 

To reach the most optimal performance, both the PCIe slot and expansion card have to be the same generation. For example, installing a PCIe 3.0 x16 graphics card into a PCIe 3.0 x16 slot on your motherboard would be ideal.

This way, you will be able to utilize the full power of the GPU.

PCIe 2.0 was released in 2007, while PCIe 3.0 was released in 2010. Furthermore, PCIe 4.0 came out in 2017, and PCIe 5.0 expects to make its way into markets in 2022.

What is PCIe?

Close up PCI Express slots on motherboard

PCIe, or PCI express, is the interface used to plug modern expansion cards into motherboards.

PCIe was released to replace PCI and AGP completely. This was highly convenient because AGP was only used for graphic cards, and PCI was used for everything else.

Now, PCIe works with nearly everything, such as graphics cards, sound cards, network cards, and so forth.

Every desktop motherboard has several PCIe slots that are used to add external components.

For this reason, PCIe lanes offer key functionality because you can easily upgrade your PC by adding new expansion cards.

As soon as a computer is turned on, the PCIe instantly identifies what devices are connected to the motherboard and creates a map of all the links. Then, all the parts connect as a whole through the motherboard, and your computer will be able to work.

PCIe Lanes Explained

Although PCIe slots are universal, they are available in a variety of different physical configurations.

The most common are x1, x4, x8, and x16. All of these types have different slots on the cards themselves and different slots on the motherboard.

They are also sized differently, with x16 being the most extended lane.

However, PCIe slots are upwards and downwards compatible. This means you can plug a PCIe 1x card into a 16x slot. It gets the same power delivery but gets less bandwidth delivered to it.

You can also plug a PCIe 8x card into a PCIe 4x slot. It will still work but will only have half of the bandwidth available.

PCIe Versions and their Bandwidths

Another thing that affects the performance of PCIe is the generation.

  • PCIe 1.0 – 250 MB/s x1 lane configuration
  • PCIe 2.0 – 500 MB/s x1 lane configuration
  • PCIe 3.0 – 1 GB/s x1 lane configuration
  • PCIe 4.0 – 2 GB/s x1 lane configuration
  • PCIe 5.0 – 4 GB/s x1 lane configuration

As you can see, each newer generation of PCIe essentially doubled the amount of available bandwidth per lane.

As such, since PCIe generations are compatible, you would be able to install a PCIe 2.0 x16 expansion card into a PCIe 3.0 x8 slot. Both of these slots offer the same amount of bandwidth, and you’d be able to save eight PCIe lanes in your motherboard.

For this reason, PC component manufacturers can ultimately make high-performing devices that use fewer PCIe lanes with each new PCIe generation.

Furthermore, smaller devices lead to less heat production and power consumption. So, manufacturers end up saving costs on building the smaller expansion card.

The difference between PCIe 3.0 and PCIe 2.0 is not just related to speed but also how it shapes the entire PC ecosystem.

Popular Uses for PCIe Slots

PCIe slots offer a lot of functionality and versatility in terms of what expansion cards you can install.

Let’s discuss the most common uses PCIe slots have.

1. Upgrade GPU and Sound Card

The most common use of PCIe slots is adding a new graphics card to your computer.

Graphics cards typically use an x16 PCIe slot, but you should also confirm the PCIe generation is the same on your computer’s motherboard.

Furthermore, you can improve your computer’s sound quality with a newer generation sound card.

If your computer currently uses an integrated graphics card and sound card, newer upgrades could boost your gaming experience exponentially.

2. Add a Video Capture Card

If you enjoy live streaming, you can add a video capture card that allows you to stream your gameplay in HD.

3. Improve Your Network

You can upgrade your internet capabilities with a new WiFi card or network card. As gamers, I typically recommend using a USB plug-in through a network card. However, there are high-end WiFI cards that you can insert into PCIe slots that offer fast connections.

Furthermore, most WiFi cards offer built-in Bluetooth capabilities. So, you’ll get the best of both worlds with a new WiFi expansion card.

4. Increase Your Memory

If your computer has low storage available, it’s highly recommended to add additional memory to your computer. PCIe slots offer the ability to add lightning-quick SSD cards. In fact, I recommend using an M2 NVMe SSD expansion card for the fastest transfer rates available.

Similarities Between PCIe 2.0 vs 3.0

Knowing what the similarities are between both generations will give a better idea of how PCIe works. This will also help you in your PC building journey.

Physical Dimensions

No matter what generation the PCIe slot is, they all have the same dimensions and physical shape.

The size and connectors are all the same, which means you can easily plug a PCIe 3.0 expansion card into a PCIe 2.0 slot.

However, the older generation slot can act as a bottleneck since PCIe slots work at the speed of the least powerful of the two.

Furthermore, you should keep in mind that expansion cards often don’t saturate the entire bandwidth of the PCIe slot. For example, a 1 GB/s network card that’s installed on an x1 slot can theoretically have a transfer speed of 125 MB/s. This is much lower than the bandwidth on a single PCIe 2.0 or 3.0 lane.

Cross-Compatability

As I mentioned before, PCIe 3.0 and 2.0 slots and devices can be used together. Any generation PCIe slot is compatible with any generation PCIe card.

However, using mismatched generations can cause bottlenecks and underutilization.

It’s typically not a good idea to use vastly different generations in your PC build. Just because they are compatible doesn’t mean you’ll be getting the most out of your computer.

If you were to install a premier GPU PCIe 3.0 x16 card on a PCIe 2.0 x16 slot, it would only have half the speed and bandwidth it was designed for. This can lead to intense bottlenecks as you’re gaming or rendering videos.

For this reason, it’s essential to use a motherboard with PCIe slots that fully capture the potential of your expansion cards.

PCIe 2.0 vs 3.0

Now, let’s take a closer look at the critical differences between PCIe 2.0 and PCIe 3.0.

1. PCIe Lane Speeds

Each newer generation of PCIe offers double the bandwidth and speed of the previous generation. So, PCIe 2.0 lanes have a bandwidth of 0.50 GB/s, while PCIe 3.0 lanes offer a bandwidth of 0.985 GB/s.

The doubling of transfer rates is an excellent reason for upgrading your computer components.

2. Expansion Card Usage

The specific version of the PCIe slot can directly affect expansion cards.

For example, a PCIe 3.0 M2 NVMe SSD expansion card takes uses an x4 PCIe lane. However, it can only inhabit older generation SSD cards such as the Samsung 970 Evo, which has a read speed of 3.5 GB/s.

However, the NVMe SSD expansion card can be installed with newer generation SSD cards like the Samsung 980 Pro PCIe 4.0, which can read speeds of 7.0 GB/s.

Furthermore, the size and lanes an expansion card occupies can also change with each newer generation. For example, an expansion card made for PCIe 2.0 x8 would perform the same on a PCIe 3.0 x4 slot.

3. Encoding

The manner in which data is encoded dramatically affects the overall bandwidth of any competent utilizing PCIe.

As such, PCIe 2.0 uses an 8b/10b encoding system. This means that for every ten bits that are transferred from the source to destination, eight bits are the data, and the remaining two bits are considered overhead. Since 20 of the total transmission is overhead, this is not particularly efficient.

PCIe 3.0 encodes data with a 128b/130b encoding system. This means that the ratio of the overhead is monumentally decreased.

For this reason, PCIe 3.0 can reach a higher bandwidth without ultimately doubling the transfer rate.

Furthermore, PCIe 2.0 offers a maximum transfer speed of 5.0 GT/s, while PCIe 3.0 offers a full transfer speed of 8.0 GT/s. Even though the bandwidth is doubled across each PCIe lane from 2.0 to 3.0, the actual transfer rate isn’t doubled. The use of a more efficient encoding system is what reduces transfer overheads.

4. Power Usage

PCIe 3.0 is much more efficient than PCIe 2.0 because it can transfer more data per clock cycle. This also means that PCIe 3.0 offers more efficient power consumption.

5. Extended Use

Although PCIe 2.0 and 3.0 are compatible with any generation of PCIe, it’s recommended to go with a PCIe 3.0 motherboard rather than 2.0.

The third generation of PCIe provides faster speeds that are better suited for gamers and video renderers. Furthermore, you might not be able to utilize your expansion cards using a PCIe 2.0 motherboard entirely.

Since PCIe 2.0 was released in 2007, most expansion cards are using newer generations of PCIe slots.

Bottlenecking your expansion cards because of an older generation motherboard deteriorates the performance and efficiency of your PC build.

If you’re trying to build a high-end gaming PC, I would even recommend opting for a newer PCIe 4.0 motherboard. This newer generation will be able to take full advantage of premium graphics cards and other expansion components.

Conclusion

At this point, you should have a thorough understanding of the differences and similarities between PCIe 2.0 and 3.0.

The newer generation offers double the bandwidth capabilities and is better suited for more recent expansion cards.

However, all PCIe generations are compatible, so you’ll be able to use each device and slot together without any issues.

If you want to know how many PCI-e express cables you need, check this article.

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