The primary difference between PCIe 3.0 vs 2.0 is the bandwidth. PCIe v3.0 has twice the bandwidth as compared to its older v2.0 counterpart.
PCIe 2.0 has a bandwidth of 0.50 GB/s per PCIe lanes. PCIe 3.0, on the other hand, offers 0.985 GB/s per PCIe lane.
In addition to that, PCIe 2.0 is also three years older than its 3.0 counterpart. PCIe 3.0 was first introduced in 2010. PCIe 2.0 was introduced back in 2007.
As far as the physical shape and look of the slots go, they are the same. Just as with PCIe 2.0, you can find PCIe x16, x8, x4 and x1 slots on motherboards with PCIe 3.0 protocol as well.
It should be noted that the PCIe 3.0 is not the latest PCIe protocol available. This has already been superseded by PCIe 4.0 and you can find plenty of boards featuring bandwidths twice as high as the PCIe 3.0 across their PCIe lanes.
What are PCIe Lanes?
In order to understand the primary difference between the version of PCIe protocols, you need to have a good grasp of what PCIe lanes are.
Basically, a PCIe lane helps in facilitating the connection between an expansion card like a graphics card, with the CPU for processing the data generated.
The amount of PCIe lanes you have at your disposal for installing expansion cards is limited. The total amount depends on your processor model and the motherboard chipset.
For instance a typical PC can provide 20 PCIe lanes to the user (newer gen CPUS and motherboards offer more). 16 of these lanes are almost always occupied by the graphics card on the primary x16 slot, whereas the rest of the 4 can be used for other devices like network adapter, video capture card, PCIe splitters etc.
Due to the limited nature of the PCIe lanes, they are kind of precious, particularly if you want to add a lot of devices to your system.
The overall bandwidth at which the connected device transfers data depends upon how many PCIe lanes it occupies AND the version of the PCIe protocol on the motherboard.
PCIe Version and their Corresponding Throughput
The table below summarizes the throughput rate (speed) of x1, x4, x8 and x16 slot on different PCIe versions.
The version of the PCIe slot and the device has far reaching ramifications both in terms of performance as well as in terms of the device’s size.
For instance, an x16 PCIe expansion card designed for PCIe v2.0, would technically perform the same if it were to be connected to an x8 slot on PCIe v3.0 slot. This in return would save up 8 of your PCIe lanes!
Thus, manufacturers can essentially make high performance devices that utilize fewer PCIe lanes with each consecutive upgrade in the PCIe version.
Smaller devices, means lower heat production, which in turn means lower power consumption and smaller sub-components used, i.e smaller heat sinks, smaller capacitors, which can ultimately end up saving up on the manufacturing and the operating cost of the expansion card.
Hence, the difference between PCIe 3.0 vs 2.0 is not just limited to the speed, but also relates to how it shapes the overall PC market.
This does not just apply to PCIe 3.0 vs 2.0 but with respect to all PCIe generations upgrades.
What are Their Similarities?
Understanding the similarities may provide some perspective into how the PCIe interface works. This could help you with your PC builds.
PCIe slots, no matter the generation, have the same size and physical shape. The motherboard above shows two PCIe x16 v2.0 and two PCIe x1 v2.0 slots.
As far as the physical size goes, the x1 and x16 slots conforming to PCIe v3.0 and V4.0 are also the same.
PCIe 3.0 and 2.0 are part of the PCIe standard although they are two different generations of the same. Their connectors on both the expansion devices and the slots are physically similar.
This means that if you have a motherboard that is running the older generation PCIe 2.0 slots and but have a newer generation PCIe 3.0 card in hand, you can still install them on the board and they will work just fine.
The only problem will be that the device and the slot work at the speeds of the least powerful of the two. So in this case, if you were to install a PCIe 3.0 device on a PCIe 2.0 slot, it will work, but at the slot can be a bottleneck.
Often expansion cards do not saturate the entire bandwidth of the PCIe slots. For instance, an 1Gbps Ethernet Card that connects to an x1 slot can have a theoretical max transfer speed of 125 MB/s. This is far lower than the bandwidth of a single PCIe 3.0 or even a PCIe 2.0 lane.
Hence a card like this would not even saturate a single lane. This brings us to the next important point, cross compatibility.
While PCIe 2.0 and 3.0 slots and devices can be used together, both these generations happen to be compatible with those that preceded them as well as those that came after them.
This means that a PCIe 3.0 device can work on a PCIe 2.0 slot. Similarly, a PCIe 2.0 device can work on a PCIe 3.0 slot.
Unfortunately this brings us to another point: underutilization vs bottleneck.
While it is true that PCIe slots and devices are cross compatible, it is not the efficient way to build your system.
If you install a high performance PCIe 3.0 x4 device like an M.2 SSD expansion card, on a PCIe 2.0 x4 slot, it would technically have half the speed it was designed for, thus bottlenecking the performance.
On the other hand, if you were to install a PCIe 2.0 x4 device, on a PCIe 3.0 x4 slot, it would underutilize the more powerful and newer slot.
- Can I Use a PCIe 3.0 Card in a 2.0 Slot?
- Can PCIe X1 Card Fit in X4 Slot?
- How to Add More PCIe Slots?
PCIe 3.0 vs 2.0
Let’s take a finer look at these two on a head-to-head comparison.
1. PCIe Lane Speeds
The first and foremost important difference between the two is that the V2.0 has a bandwidth of 0.50 GB/s whereas the newer V3.0 has 0.985 GB/s bandwidth.
This follows the idea that each consecutive PCIe generation doubles the bandwidth available per lane.
2. Ramification on the Device Size and Speed
While not directly related to the PCIe bus and slot on the motherboard, the version of the PCIe can have a direct impact on the expansion cards.
For instance, a PCIe V3.0 M.2 NVMe SSD Expansion Card take up x4 PCIe lanes. However, it can only occupy older gen SSDs like the Samsung 970 Evo which has a read speed of 3.5 GB/s.
On a PCIe V4.0, the NVMe SSD Expansion card can be installed with newer gen SSD like the Samsung 980 Pro which can reach speeds of 7.0 GB/s (double the speed of the previous gen SSD).
The image above shows a typical M.2 NVMe SSD Expansion Card for x4 PCIe slot. Source: Rivo
In addition to speed, the size and the lanes a device occupies also can change with each consecutive generation. For instance, an expansion card that is designed to use EIGHT V2.0 PCIe lanes, would perform the same on a slot with FOUR V3.0 PCIe lanes if it were to be redesigned with an V3.0 x4 connector.
3. Encoding – For the Advanced Users
How the data is encoded has a great impact on the overall bandwidth of any device including that of the PCIe protocol.
PCIe 2.0 makes use of an 8b/10b encoding system. What this means is that for every 10 bits that are transmitted from source to destination, 8 bits are the data and the remaining 2 bits (20% of the total transmission) are considered overhead. This not very efficient.
With PCIe 3.0, the data is encoded using a much more efficient 128b/130b encoding system. The ratio of the overhead here is much lower.
As such, through a better encoding algorithm, PCIe 3.0 can achieve a higher bandwidth without essentially doubling the transfer rate.
PCIe 2.0 supports a max transfer speed of 5.0 GT/s (Giga Transfers per second) whereas the PCIe 3.0 supports a max transfer speed of 8.0 Giga Transfers per second. Note that despite doubling the bandwidth across each PCIe lane, the actual transfer rate isn’t doubled (i.e it is not 10 GT/s). This is thanks to the better encoding which reduces transfer overheads.
This brings us to the next point:
4. Lower Power Usage
So, as mentioned earlier, PCIe 3.0 doubles the bandwidth without doubling the actual transfer rate (due to a better encoding algorithm). Meaning, it can transfer more data per clock cycle compared to the previous generation. As a result of this it achieves a higher efficiency.
This also results in a direct improvement on the power consumption.
Lower transfers -> lower power consumption -> smaller electrical sub-components required -> cheaper expansion card
5. Extended Use
Both PCIe 2.0 and 3.0 are compatible with all other generations of the PCIe standard, however, for users hoping to get the best performance over time from their system and keep up with the trends in the PCIe arena, it is best to go with a PCIe 3.0 motherboard over a PCIe 2.0 motherboard for several reasons.
The first reason is that the third generation is much faster, you get to enjoy better speeds. High transfer rates mean that for applications like video rendering or gaming, you get better performance from PCIe 3.0.
Also, because newer devices that come out are much faster, if you have a motherboard with PCIe 2.0 slots, you will end up not fully utilizing some of your newer generation cards.
The older 2.0 slot will bottleneck the newer 3.0 card’s performance hence you may end up underutilizing it.
All this goes to show that when it comes to computers, sometimes newer is always better.
In fact, I would recommend that you also consider the newer PCIe v4.0 motherboards. While not essential for basic use case at the moment, if you are building a performance or a gaming PC, then a PCIe v4.0 is highly recommended.
After this lengthy discussion about PCIe 3.0 vs 2.0, we have seen that with the upgrade in generations, we also get an increase in the performance of the components.
PCIe components are cross-compatible, meaning that regardless of what generation you have, whether a 2.0 or a 3.0, you will still be able to use the different slots and devices together without much of a hassle.
One thing you’ll need to note, is that sometimes the motherboard may offer two different PCIe protocols at the same time for its different slots.
For instance, the AMD A320 motherboards offers PCIe v2.0 for slots connected to the motherboard chipset and PCIe v3.0 for the x16 slot connected to the CPU.
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