The answer is yes, a Gen 4 M.2 will work in a Gen 3 slot because PCIe slots are both forward and backward-compatible, which means you will be able to use any generation of M.2 device on your system.

But before we dive into the technical details of Gen 4 M.2 devices, let’s first refresh our memories about what these terms actually mean.

What Is PCIe 4.0?

PCI-Express (PCIe) is a commonly used electrical bus that can be found on almost every PC and laptop nowadays. PCIe slots on computers allow the user to connect a variety of different components to their system, like storage devices, sound cards, video capture cards, graphics cards, network cards, etc. 

What Is M.2?

M.2 is a compact form factor that is typically associated with current-gen PC storage devices – SSDs, to be more exact. This is because hard disk drives cannot achieve the same low-profile form factor as an SSD.

Moreover, M.2 cards directly connect to the motherboard using an M.2 connector. But do make sure that your motherboard supports the form factor when purchasing an M.2 device, as they come in various lengths. 

How Fast Is PCIe Gen 4 In Comparison to Gen 3?

Each new generation of PCIe has approximately double the bandwidth of the previous generation. Hence, when putting up PCIe Gen 4 devices against Gen 3 devices, Gen 4 devices can benefit a lot from the increased bandwidth, which could come in the form of faster storage speeds, faster load times, etc. 

Here is a comparison of the speeds between PCIe Gen 4 vs Gen 3. 

Which CPUs Support PCIe Gen 4?

Intel first introduced PCIe 4.0 support for its 11th generation “Rocket Lake” processors. Whereas AMD began supporting PCIe 4.0 with its Ryzen 3000 and 5000 processors, which was later followed by the Ryzen Threadripper 3000 series and the Ryzen Threadripper Pro 3000 series. 

Which Motherboards Support PCIe Gen 4?

To get full PCIe 4 support from Intel’s 11th generation of processors, you will need a motherboard with the Z590 or B560 chipset. On the other hand, you will need a motherboard with the X570 chipset for full PCIe 4 support if you are going with AMD processors. 

How Will A Gen 4 M.2 Perform In A Gen 3 Slot?

A Gen 4 M.2 will be limited to the speed of a Gen 3 slot, which means the maximum speed you can attain from a Gen 4 M.2 device will be capped at the maximum speed of the Gen 3 slot. 

To better understand this concept, we need to look at an example. Let’s take the Samsung 1 TB 980 PRO PCIe 4.0 NVMe M.2 SSD. This storage device has a maximum read speed of 7000 MB/s, which can only be achieved using a PCIe 4.0 slot.

So, if you were to use it in a dual-lane PCIe 3.0 slot, then the SSD would top out at 2000 MB/s. As a result, you are going to get much slower speeds during data transfer. 

Should You Use Gen 4 M.2 In A Gen 3 Slot?

If possible, then it is recommended that you use a Gen 4 M.2 device in a Gen 4.0 slot, as this will give you the best possible performance and speed. However, if you do not have access to a Gen 4 slot, then you can use a Gen 3 slot.

Although there is a speed gain when using Gen 4 instead of Gen 3, it’s not really possible to tell them apart in regular day-to-day tasks. Hence, you should be fine with using a Gen 4 M.2 device on a Gen 3 slot.