In this article, we’ll look at the fundamental differences between PCIe 2.0 and 3.0 and some specific examples of those differences.
If you are looking for a quick answer about the differences between PCIe 2.0 and PCIe 3.0, it is that PCIe 3.0 is twice as fast as PCIe 2.0.
This is because the bandwidth of PCIe 3.0 is 0.985 Gigabytes per second (Gb/s) per lane and the bandwidth of PCIe 2.0 is 0.5 Gigabytes per second (Gb/s) per lane.
But if you want to know some geeky details, continue reading! We are going to start from the basics and work our way up to the more complex things.
We will start with some definitions, and then we’ll look at some examples and benchmarks of PCIe 3.0.
If you already know all there is to know about PCIe, feel free to jump around on this page; however, you may find some interesting facts that you didn’t know before.
What Is PCIe?
The PCI- Express specification is an expansion card interface standard for connecting different computer peripherals to computers and host computers. It is a high-speed computer expansion standard intended to replace older technologies like the PCI and AGP bus standards.
It is found on motherboards in desktop, laptop, and server computers and is used to add peripheral devices such as graphics cards, network connections, high-speed storage devices, and other peripherals that require high bandwidth.
The PCIe specification was created by Intel Corporation in 2003 and is now available from the PCI Special Interest Group (PCI-SIG). The PCIe specification includes the base specification and several different versions with different transfer speeds. The most common implementations are 1.0, 2.0, 3.0, 4.0 and 5.0.
Related Article: What Are PCIe Slots? Ultimate Guide
WHAT ARE PCIe LANES?
To understand the difference between PCIe 2.0 and PCIe 3.0, you first need to understand what the term “lane” means in reference to PCIe.
A PCIe lane is a single hardware channel that carries all data traffic between the chipset and the PCIe peripherals.
The number of PCIe lanes of your computer is determined by your motherboard and chipset, and the PCIe lanes are divided among the devices you have installed. In other words, it is possible that your motherboard supports up to 20 PCIe 3.0 lanes, but you can only use 8 for your graphics card (standard primary slot) because the rest are being used by other devices like your network card, sound card, or other slots.
Related Article: How Many PCIe Lanes Does Ryzen Have? [Solved]
What is PCIe bandwidth?
Now that you know what a PCIe lane is, you can understand what PCIe bandwidth is.
The PCIe bandwidth is the number of gigabytes per second that the channel can carry between the chipset and the peripheral device and is determined by the PCIe version and the number of lanes.
For example, if you have a PCIe 2.0 x16 slot and plug a graphics card (GPU) into it, the bandwidth will be 8 GB/s because the current version of PCIe is 2.0 and has a bandwidth of 0.5GB/s per lane; it has x16 lanes (the highest number on a slot) which equals 8 GB/s.
Below you can see a table with all the PCIe bandwidths to understand the difference between different versions:
|Generation||x16 GB/s||x8 GB/s||x4 GB/s||x2 GB/s||x1 GB/s|
Related Article: What Are PCIe x1 Slots And What They Are Used For
PCIE 2.0 VS PCIE 3.0 Differences
Now that you know what PCIe lanes, bandwidth, and versions are, it is time to talk about the differences between PCIe 2.0 and PCIe 3.0.
The main difference between PCIe 2.0 and PCIe 3.0 is the speed.
PCIe 2.0 has a bandwidth of 0.5GB/s per lane, while PCIe 3.0 has double that at 0.985GB/s per lane. This means that PCIe 3.0 is two times faster than PCIe 2.0.
For example, if you have a PCIe x16 slot (which is the highest number on an expansion slot), with PCIe 3.0 the bandwidth would be 15.754 GB/s and only 8 GB/s with PCIe 2.0.
2. Expansion Card Speed
This isn’t directly related to the speed of PCIe 3.0 itself, but it can affect it.
I am going to use an example to clarify what I mean because it is a bit confusing.
Let’s say you buy a PCI e 3.0 expansion card that can use up to 4x lanes. This means that it should have a bandwidth of 4 * 0.985 GB/s = 3.940GB/s, right? But if it can only be used with older SSD models that don’t have such a high bandwidth capacity, it won’t be able to reach its max speed. That makes sense, right?
On the other hand, a PCIe 4.0 expansion card and a newer SSD will have a higher bandwidth capacity and run faster.
I gave you these examples to make you understand that the older the PCIe version is, the lower the speed of the devices that were designed for it will be.
3. More Efficient Power Usage
The PCIe 3.0 has more efficient power usage than PCIe 2.0.
The main reason is that the PCIe 3.0 can double the bandwidth without doubling the transfer rate. This means you can transfer two times the amount of data simultaneously, resulting in lower power consumption.
Because the data transfers are lower with PCI 3.0, it uses less power to do so.
4. Better Encoding
This is a bit advanced topic, so I will try to make it as clear as possible.
PCIe 3.0 uses a more efficient encoding scheme than PCIe 2.0.
What does this mean?
The PCIe 2.0 uses the 8b/ 10b encoding system. This means for every 10 bytes it sends, 8 are used for data, and 2 are overhead. So 20% of the data sent is overhead and can’t be used.
However, with PCIe 3.0, the encoding scheme has been changed to 128b/130b, meaning that for every 130 bytes it sends out, 128 are data, and 2 are overhead.
This means that the amount of data sent is much higher compared to PCIe 2.0, and therefore you can transfer more data in less time.
To understand further how important the encoding scheme is, let’s talk about the transfer speed difference between PCIe 2.0 and PCIe 3.0:
The maximum transfer speed of the PCIe 2.0 is 5 Giga Transfer per second (GT/s); as you already know, the PCIe 3.0 has double the speed that the PCIe 2.0 has, so you would expect the maximum transfer speed of PCIe to be 10 Giga Transfer per second (GT/s). That makes sense, right?
Well, unfortunately, it is not that simple.
The maximum transfer speed of PCIe 3.0 is 8 Giga Transfer per second (GT/s). But why?
The reason is because of the encoding scheme. As you already know, PCIe 2.0 uses the encoding scheme I mentioned above that has a 20% overhead, but PCIe 3.0 can get rid of that overhead, and therefore it is able to use the full capacity of the lanes, which results in double speed compared to PCIe 2.0. You can learn more by reading our article: “Can I Use PCIe 3.0 In 2.0 Slot?“
5. Longer life
While both PCIe 3.0 and 2.0 can be used with other versions, the PCIe 3.0 will have a longer life span.
I know that this is a bit vague, but I will try to explain myself.
The first reason for this is because the PCIe 3.0 is faster than PCIe 2.0, and therefore if you want to do difficult tasks like running a Virtual Machine or rendering, the PCIe 2.0 won’t be able to cope with the requirements, and you will need to upgrade to a PCIe 3.0 slot.
The second reason is that technology is moving forward quickly, and the demands are getting higher and higher because of that.
This means that new devices require specific standards like PCIe 3.0, and therefore you will need this slot to properly run those devices and avoid bottlenecks, especially if they are high-demand devices such as graphic cards or SSDs.
So to summarize this, using the old PCIe 2.0 will leave you with limited speed and compatibility in future devices/tasks, so I recommend you to purchase a PCIe 3.0 or above.
Related Article: Does it matter which PCIe x16 slot I use?
Similarities between PCIe 2.0 and PCI 3.0
We have talked a lot about all the differences between PCIe 2.0 and PCIe 3.0, now, let’s talk about the similarities between them.
The first and most obvious similarity between the two standards is their physical size.
Both PCIe 2.0 and PCIe 3.0 slots are identical in size.
This means you can install any PCIe 3.0 card in a PCIe 2.0 slot and vice versa without having any issues since they are the same size.
When I say you won’t have any issues, I’m not saying you will be able to get the full speed of the slot. All I’m saying is that it will work because the slot is physically compatible.
A solution to this problem using an expansion card. An expansion card is a small circuit board used to extend the capabilities of a computer system. This allows you to get the full speed of your PCIe 3.0 or card slot, even if it is installed in a PCIe 2.0 or 1.0 slot. But you should keep in mind that even with expansion cards, the speed will be lower than the maximum transfer speed of your PCIe slot.
2. Cross Compatibility
I already mentioned that a PCIe 3.0 device could run in a PCIe 2.0 slot and vice versa, but I never mentioned if it will be able to give you the full potential of your device.
As you already know, PCIe 3.0 has double the maximum transfer speed of PCIe 2.0, and therefore you should not expect the full potential of your device by installing it in a PCIe 2.0 slot, even with an expansion card installed.
Related Article: What Is A PCIe Cable And What It Is Used For
We have covered the main differences between PCIe 2.0 and PCIe 3.0, but I want to briefly summarize everything.
The main difference between these two PCIe slots is the maximum transfer speed, which in simple words, means that you have double the speed using PCIe 3.0 instead of PCIe 2.0. This also affects compatibility, so while both are physically compatible, your devices will not have the full speed in a PCIe 2.0 slot.
If you want to use future graphics cards or other high-demand devices, I recommend you go with a PCIe 3.0 as it will give you the full potential by using only one slot, and it is the standard of today’s technology.
However, PCIe 2.0 will do the job just fine if your device isn’t that demanding or on a tight budget.
Something I forgot to mention is that there are faster versions of PCIe (than PCIe 3.0), such as PCIe 4.0, and if you work in a demanding area, you should definitely go with PCIe 4.0 or above if your motherboard supports it.
I hope that this article gave you a good insight into the main differences between PCIe 2.0 and PCI 3.0 standards, and I also hope you liked it.
If you still have any questions, ask in the comments section below, and I will be glad to answer you.
Nick Ryley is a computer architect and the owner of The Pc Geekz.
His love for playing games got him interested in computers in the first place. He wanted to be able to build a gaming PC that could run all the latest games at max settings, and this has him pursuing a major in computer architecture!
He started this blog to help people out and answer some of the most common questions about computer building