# Asrock B550 motherboards M.2 slot question



## Buftor (Jun 12, 2020)

I am planning to use two NVME drives, so I checked the specs of the M.2 slots in B550 motherboards. With most brands, I found that the primary M.2 slot supports PCIE4x4 and the secondary supports PCIE3x4. However, with Asrock boards, I noticed that on all B550 boards (except for the Taichi) the second M.2 slot is rated at only PCIE3x2 (16Gbs), not PCI3x4 (32Gbs). It seems weird to me. Is it possible that there's an error in the specs? This will affect my purchase decision, so thanks for any input.


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## puma99dk| (Jun 12, 2020)

You need to be more specific with what B550 model from AsRock you want to buy and use because this time around AMD gives the manufactures more options on how to use PCI-E lanes from the CPU.

Most B550 board will have the top M.2. slot as PCI-E Gen4 and the top PCI-E x16 as Gen4 everything else is Gen3.


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## TheLostSwede (Jun 12, 2020)

Buftor said:


> I am planning to use two NVME drives, so I checked the specs of the M.2 slots in B550 motherboards. With most brands, I found that the primary M.2 slot supports PCIE4x4 and the secondary supports PCIE3x4. However, with Asrock boards, I noticed that on all B550 boards (except for the Taichi) the second M.2 slot is rated at only PCIE3x2 (16Gbs), not PCI3x4 (32Gbs). It seems weird to me. Is it possible that there's an error in the specs? This will affect my purchase decision, so thanks for any input.


Not weird at all, it depends what they've allocated the PCIe lanes to. In fact, a lot of early M.2 implementations were like that, due to lack of PCIe lanes from the chipset.


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## Flaky (Jun 12, 2020)

I've also noticed that Asrock made this weird design choice. 
I don't think there's an error in specs - most boards fully utilize all, or most of the platforms I/O, leaving no "dangling" 2 PCIe lanes.

It's one of the reasons I don't even consider buying or recommending their B550 boards.

But, If you really want a B550 Asrock, and need second M.2 with 3.0 x4 link, just grab a cheap adapter.


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## Assimilator (Jun 12, 2020)

Buftor said:


> Is it possible that there's an error in the specs?



Possible yes, likely no. Asrock is using those extra lanes to add more features (2.5Gb or 5Gb networking, or more USB ports) or they buggered up their implementation, but either way that's not the kind of typo they would make.


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## newtekie1 (Jun 12, 2020)

When the chipset only puts out 6 PCI-E 3.0 lanes and only 4 lanes if you choose to add an extra 2 SATA ports, things have to be cut.  To me, it makes sense to cut the 2nd M.2 slot down to x2 since most people would never even notice the difference in performance on a secondary drive.


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## Flaky (Jun 12, 2020)

newtekie1 said:


> When the chipset only puts out 6 PCI-E 3.0 lanes and only 4 lanes if you choose to add an extra 2 SATA ports (...)


B550 puts out more. The numbers you're referring to are from incorrect slides that many reviewers did receive.
The actual numbers that other resources provide, and make much more sense (after seeing b550 boards specs) are 8 PCIe lanes + (2 PCIe lanes OR 2 SATA).

Only Asrock decided to limit second M.2 to x2. All other manufacturers are fine with x4. 
The only benefit of such decision is having x16@x4 slot completely independent from x1 slots.


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## Buftor (Jun 12, 2020)

First, thank you all for your replies.
The only reason I am considering B550 over B450 is the availability of two PCIE M.2 slots. I always run out of storage. I bought a PCIE3 M.2 drive for this new computer, and plan to add PCIE4 drive in the future.
I made a shortlist of MB from all brands that meet my requirements (number one: it has to be mATX size). One of boards on my shortlist was Asrock B550M Steel Legend. I was surprised to read that the second M.2 slot has only two lanes. All the boards from other brands have 4 lanes, even the most basic models. So I checked each and every B550 board from Asrock to see if it's an error in the specs. I found that only the most expensive Taichi has 4 lanes. Every other B550 model from Asrock has only two lanes. I guess, as a few of you said, it is indeed a weird design choice.


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## TheLostSwede (Jun 12, 2020)

Buftor said:


> First, thank you all for your replies.
> The only reason I am considering B550 over B450 is the availability of two PCIE M.2 slots. I always run out of storage. I bought a PCIE3 M.2 drive for this new computer, and plan to add PCIE4 drive in the future.
> I made a shortlist of MB from all brands that meet my requirements (number one: it has to be mATX size). One of boards on my shortlist was Asrock B550M Steel Legend. I was surprised to read that the second M.2 slot has only two lanes. All the boards from other brands have 4 lanes, even the most basic models. So I checked each and every B550 board from Asrock to see if it's an error in the specs. I found that only the most expensive Taichi has 4 lanes. Every other B550 model from Asrock has only two lanes. I guess, as a few of you said, it is indeed a weird design choice.


Keep in mind that a lot of B550 have split features, due to the lack of PCIe lanes from the chipset. I guess what ASRock was, was to enable the second M.2 slot at all times, without disabling something else, whereas other board makers would let you chose between it, or say a PCIe x4 slot or something similar. Again, this is not uncommon from ASRock's side, from what I've seen. Gigabyte seems to be doing the same on the B550M Aorus Elite.


> Supporting SATA and PCIe 3.0 x2 SSDs


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## Buftor (Jun 12, 2020)

TheLostSwede said:


> Gigabyte seems to be doing the same on the B550M Aorus Elite.



Thank you for your answer. The specs of the Gigabyte mATX boards were only revealed today. I see that the B550M Aorus Pro is the only model with secondary M.2 Gen3x4 slot. That one will definitely be on my shortlist.


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## puma99dk| (Jun 12, 2020)

Do you in reallity need PCI-E 4gen NVME SSD? A lot of users with a recently new platform feel that a SATA SSD is has the same responsive feel or even better because they have a hard time telling them apart.

Linus Tech Tips actually tested this like 3 months ago and even his employee's couldn't really tell which was which.









Personally for me if I could get a 2 and 4TB SATA SSD's with DRAM cache for a better price then what they are now and like £100 a part when I look at prices for SATA vs NVME 2TB drives.


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## tabascosauz (Jun 12, 2020)

Do you actually do sequential writes all day, though? 16Gb/s is still a theoretical cap of 2000MB/s; how often do you hit that number in sequential writes on a daily basis? For most users, random performance rules day-to-day activities at far below 2000MB/s. You've got more important and relevant performance considerations than a theoretical number you won't be using if you're an average user.

The Aorus Pro M and Steel Legend M are hardly even competitors apart from their form factor, and if they turn out at the same price point Gigabyte would be rather misguided. The former has a 1Gbe Realtek (not even Intel) while the latter has a 2.5Gbe Realtek, a headlining feature for most B550 boards. I'm 95% sure the former is recycling low end Gigabyte's favourite hot 4C06/4C10 MOSFETs under those blocky heatsinks, while the Steel Legend looks to be using the same 50A Vishay DrMOS found on entry to midrange X570s.

Don't forget that the Steel Legend has three M.2 slots; it not only has a small dedicated E-key slot for Wifi cards, but also has the requisite cutouts in its I/O to add the antennas. It's pretty clear to see that these two are miles apart in their target segment. While neither has a POST code, the Clear CMOS on the I/O of the ASRock is the equivalent of having one of those overclocking buttons on higher end boards. Just some info to take into account when you're deciding how important having two x4 slots is to you.


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## Buftor (Jun 12, 2020)

tabascosauz said:


> Do you actually do sequential writes all day, though? 16Gb/s is still a theoretical cap of 2000MB/s; how often do you hit that number in sequential writes on a daily basis?



You raise some valid points. I only do photo editing, no gaming at all. My laptop has both NVME and SATA SSD. Buzzing through thousands of photos, with file sizes up to 40MB, I can clearly see the advantage of NVME. That's why I want the desktop that I'm building to have two fast M.2 slots. I only use the network to do backups to my NAS, so that's not as critical.


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## tabascosauz (Jun 12, 2020)

Buftor said:


> You raise some valid points. I only do photo editing, no gaming at all. My laptop has both NVME and SATA SSD. Buzzing through thousands of photos, with file sizes up to 40MB, I can clearly see the advantage of NVME. That's why I want the desktop that I'm building to have two fast M.2 slots. I only use the network to do backups to my NAS, so that's not as critical.



Have you actually monitored disk usage and peak speeds during your editing workflows? I never see any significant disk usage speeds working in PS, not nearly to the point where 3.0 x2 or x4 would make a difference.

My .NEFs out of my camera are generally 30-35MB in size, and each of the resulting .PSDs anywhere between 50MB and 300MB. Regardless of whether PS 2019 is configured to use 5GB, 20GB, or 50GB of disk cache, I've not seen any measurable difference between having PS installed and files working in my SATA or NVMe on my main 3700X.

What does make a difference, however, is the actual other hardware in the system, in particular if I'm doing work on my 4790K or 3700X. The difference there is usually minor and mostly limited to startup and .NEF opening times, but certainly more noticeable than the SATA vs. NVMe difference when it comes to file saving. As long as you have a relatively recent and large (500GB-1TB) TLC SATA drive with DRAM and not an ancient X-25M, for example.

Obviously, this depends on what software you use, but Adobe software tends to lean on the CPU more. It does like GPU acceleration, however.


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## newtekie1 (Jun 13, 2020)

Buftor said:


> You raise some valid points. I only do photo editing, no gaming at all. My laptop has both NVME and SATA SSD. Buzzing through thousands of photos, with file sizes up to 40MB, I can clearly see the advantage of NVME. That's why I want the desktop that I'm building to have two fast M.2 slots. I only use the network to do backups to my NAS, so that's not as critical.



You benefit from the larger queue sizes and random reads of NVMe, not the large sequential read speeds. So the extra sequential read speed you get with x4 vs. x2 won't matter to you.


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