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PCIe 3.0 vs. 4.0: Is PCIe 4.0 Worth the Upgrade?

Updated on Jun 1, 2022
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PCIe, short for Peripheral Component Interconnect Express, is a high-speed interface standard for connecting various components of computing devices such as GPUs and SSDs. PCIe standards have different generations like PCIe 3.0 and PCIe 4.0. Currently PCIe 4.0 devices are most prevalent. Let's dive in to explore the difference between PCIe 3.0 and PCIe 4.0, and whether PCIe 4.0 is worth the upgrade.

What Are PCIe 3.0 & PCIe 4.0?

Current PCIe standards come in five generations: PCIe 1.0, PCIe 2.0, PCIe 3.0, PCIe 4.0 and PCIe 5.0. The newest standard PCIe 5.0 came out in May 2019. However, as of this writing, no PCIe 5.0 devices are currently available. The first PCIe 5.0 device is expected to debut in late 2022. Thus, PCIe 3.0 and PCIe 4.0 devices dominate the market.

PCIe 3.0

In November 2010, PCI-SIG (PCI Special Interest Group) announced that PCIe 3.0 would come with a data transfer rate of 8 gigatransfers per second (GT/s). Compared to previous PCIe 1.0 and 2.0 generations, PCIe 3.0 has a faster signal speed and a lower data transmission delay. In addition, new features for the PCIe 3.0 standard include a number of optimizations for enhanced signaling and data integrity, such as transmitter and receiver equalization, phase lock loop improvement, clock data recovery, and channel enhancements of supported topologies.

At the same time, PCIe 3.0 is both backward and forward compatible with existing PCIe devices. But the performance depends on the lowest PCIe standard generation in your implementation. For instance, a PCIe 3.0 SSD can be inserted into a PCIe 2.0 slot of a motherboard, but you will only get PCIe 2.0 performance. Likewise, a PCIe 3.0 SSD also can be inserted into a motherboard with PCIe 4.0 slot, and you will only get PCIe 3.0 performance.

PCIe 4.0

The PCIe 4.0 standard debuted in June 2017. It comes with a data transfer rate of 16 GT/s that doubles the bandwidth of PCIe 3.0. As PCIe slots can be configured with one lane or multiples of four lanes, such as x1, x4, x8, x16, this means that a PCIe 4.0 x4 interface can work like a PCIe 3.0 x8 interface and offers the same amount of bandwidth.

In addition, PCIe 4.0 still features backward and forward compatibility with other PCIe generations. Nowadays, many manufacturers have introduced various devices with PCIe 4.0 specs. For example, Mellanox Technologies released the first 100 Gbit/s network adapter with PCIe 4.0 in June 2016, and in January 2019, AMD introduced the X570 chipset and Zen 2-based processors that support PCIe 4.0.

PCIe 3.0 vs. 4.0 in Key Aspects

The differences between PCIe 4.0 & PCIe 3.0 are apparent. Let's look at them in detail from the following aspects.

Slot

Every motherboard has a number of PCIe slots used to add GPUs, SSDs, and RAID card etc. As mentioned above, a single PCIe slot can have x1, x2, x4, x8, or x16 lanes. For example, PCIe 4.0 x8 refers to a Gen 4 expansion card/slot with 8-lane configurations. The number of lanes contributes to the bandwidth scales. An 8-lane configuration has twice the bandwidth of a 4-lane configuration.

Both PCIe 3.0 and 4.0 slots can be configured with x1, x2, x4, x8, and x16 lanes, but PCIe 4.0 slots have a higher transfer rate per lane and bandwidth throughput. More specifically, a PCIe 4.0 slot has a 16 GT/s transfer rate per lane, twice the transfer rate that a PCIe 3.0 slot supports.

Speed

Speed is also a crucial factor that has a great impact on performance. To put it simply, PCIe 4.0 is twice as fast as PCIe 3.0. PCIe 4.0 has a data transfer rate of 16 GT/s data rate, while PCIe 3.0 only has an 8 GT/s data rate. Likewise, each PCIe 4.0 lane configuration supports twice the bandwidth of PCIe 3.0, topping at 32 GB/s in a 16-lane slot in unidirectional travel. The following table shows the speed differences in different lane configurations between PCIe 4.0 and PCIe 3.0.

 

Unidirectional Bandwidth: PCIe 3.0 vs. PCIe 4.0
PCIe Generation x1 x4 x8 x16
PCIe 3.0 1 GB/s 4 GB/s 8 GB/s 16 GB/s
PCIe 4.0 2 GB/s 8 GB/s 16 GB/s 32 GB/s

Compatibility

When it comes to compatibility, both PCIe 4.0 and PCIe 3.0 are backward and forward compatible with the existing PCIe configurations. We now know PCIe slots are used to connect components such as GPUs and SSDs to the motherboard so that they can function in a normal way.

With backward and forward compatibility, the new PCIe generation can be used with the old (backward compatibility), and vice versa (forward compatibility). For instance, a PCIe 4.0 GPU can be inserted into a PCIe 3.0 slot on a motherboard, but the PCIe 4.0 GPU’s bandwidth would be hindered by bandwidth limitations of the PCIe 3.0 slot.

One thing to notice is that you have to make sure that your motherboard’s slot has an equal or greater number of lanes than the PCIe card you insert into. Otherwise, you will not be able to insert your PCIe card into the slot physically. For example, a PCIe 3.0 x4 SSD card can fit in a PCIe 4.0 x4 or x8 slot, but a PCIe 3.0 x8 card won’t be compatible with an x2 or x4 slot. Therefore, you'd better check beforehand whether your PCIe 4.0 or 3.0 GPUs and SSDs are compatible with the lane configuration of your motherboard’s slots.

Price

Just like any other different product generations, price is a big difference between PCIe 3.0 and PCIe 4.0. Generally speaking, PCIe 4.0 GPUs and SSDs are always more expensive than PCIe 3.0 ones with the same storage and lane configurations. After all, PCIe 4.0 devices come with higher bandwidth and better performance. In addition, prices also vary depending on the manufacturer. You should do a thorough product analysis before making your purchase decision.

How Do PCIe 3.0 and 4.0 Affect Your SSD and GPU?

As mentioned above, both PCIe 4.0 and PCIe 3.0 are backward and forward compatible with the existing PCIe configurations. However, because of their bandwidth limitations, you won't always get the full performance of your PCIe GPUs or SSDs.

If you connect a PCIe 3.0 GPU to a PCIe 4.0 slot, you will only get the PCIe 3.0 standard performance. If you connect a PCIe 4.0 GPU to a PCIe 3.0 slot, you won't be able to cash in on the increased bandwidth and data transfer speed of your PCIe 4.0 GPU. The same thing goes for PCIe SSDs.

That said, it is not hard to see that a motherboard with PCIe 4.0 ports has an obvious advantage over those with PCIe 3.0 ones. Using a motherboard with PCIe 4.0 ports, you have more room to increase the number of SSDs and GPUs to support higher bandwidth. For instance, to achieve 16 GB/s of bandwidth, you need only 8 PCIe 4.0 lanes instead of 16 lanes with PCIe 3.0.

Is PCIe 4.0 Worth the Upgrade?

So should you upgrade to PCIe 4.0 if you are already on PCIe 3.0? We don't think PCIe 4.0 is going to render your older PCIe 3.0 useless. If you are comfortable with your current bandwidth and have no plan on spending more money to increase your bandwidth performance in the near future, you may not need to upgrade to a PCIe 4.0 motherboard that is probably not worth it to you.

In addition, if you are working with PCIe 3.0 slots and components such as PCIe 3.0 graphic cards and storage, and they’re offering the data transfer speed that your applications need, then don’t worry about upgrading to PCIe 4.0.

But if your applications soon need a bandwidth boost to keep up with an increasing workload, you may want to consider upgrading. In this case, you can always take advantage of the increased bandwidth performance that PCIe 4.0 can offer. When deciding whether to upgrade, always keep your own needs in mind instead of rushing to the newer PCIe 4.0.

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