What is: Infinity Fabric, and do I need to pick an AMD certified ram or is it all marketing.

[qboIodp]

 

I am currently buying parts for a new build and I was wondering because I know that AMD has some kind of limit on the mhz but I don't know exactly all the info. I searched a bit and I just found some old posts that were posted at the beginning of the zen 3 launch, so they didn't know much about that. Can anyone help me pick the right ram?

links to the CPU and MOBO

[svmlegacy]

Quote

do I need to pick an AMD certified ram

No.

15 minutes ago, qboIodp said:

Can anyone help me pick the right ram?

Check the QVL of the motherboard if you want guaranteed compatibility.

Most (99%) kits will work fine.

Aim for 3600 MHz with as low of a CL as you can get.

[Master Disaster]

Infinity fabric is what used to be called Front Side Bus, at the most basic level its the clock speed that the chipset uses to communicate with the rest of the system however is the case of IF its a little different since modern CPUs have the functionality of what used to be called the northbridge baked into the CPU.

 

My RAM runs at 3600Mhz effective (which is 1800Mhz actual) and IF runs at 1800Mhz which means the ASIC on the CPU is able to synchronise the data transfer on the bus between the 2 devices meaning there is no waiting between cycles for one bus to be ready.

 

Honestly, for your everyday usage its really not that important. Sure its nice to have a 1:1 ratio between the RAM clock and IF but even if you don't achieve it the difference in performance is pretty small.

 

6 minutes ago, svmlegacy said:

Check the QVL of the motherboard if you want guaranteed compatibility.

QVLs are useless. Certification comes at a cost to the manufacturer which means the only sticks that end up on a QVL are ones that manufacturers are willing to pay for the cost of certification.

 

With the exception of Zen 1 (and to a lesser extent Zen 2) CPUs, RAM is RAM and will work.

[qboIodp]

7 minutes ago, Master Disaster said:

Infinity fabric is what used to be called Front Side Bus, at the most basic level its the clock speed that the chipset uses to communicate with the rest of the system however is the case of IF its a little different since modern CPUs have the functionality of what used to be called the northbridge baked into the CPU.

 

My RAM runs at 3600Mhz effective (which is 1800Mhz actual) and IF runs at 1800Mhz which means the ASIC on the CPU is able to synchronise the data transfer on the bus between the 2 devices meaning there is no waiting between cycles for one bus to be ready.

 

Honestly, for your everyday usage its really not that important. Sure its nice to have a 1:1 ratio between the RAM clock and IF but even if you don't achieve it the difference in performance is pretty small.

I was reading on another thread about the IF and some people said that it would be a waste of having 4000Mhz ram cause it wouldn't be able to achieve that because of the IF. Is that true, should I pick 3600 as they also said? 

[Mark Kaine]

8 minutes ago, Master Disaster said:

QVLs are useless.

yeap, my ram is on the qvl, and it does work (yay?) but there is no OC headroom whatsoever, which both the RAM and the motherboard advertise as one of the main features. 

[qboIodp]

1 minute ago, Mark Kaine said:

yeap, my ram is on the qvl, and it does work (yay?) but there is no OC headroom whatsoever, which both the RAM and the motherboard advertise as one of the main features. 

so basically I should try to find a random video on yt to see what they use and if it works as it supposed to, prefer that?

[Beerzerker]

17 minutes ago, svmlegacy said:

No.

Check the QVL of the motherboard if you want guaranteed compatibility.

Most (99%) kits will work fine.

Aim for 3600 MHz with as low of a CL as you can get.

Anything that's not Corsair that is.
Some Corsair sticks work fine with Ryzen but there is a real, definite trend for Corsair and Ryzen not working well together well established by all the threads we've seen that Corsair sticks in a Ryzen build having problems.

Most anything aside from Corsair is a good bet but even then there are no guarantees but with all the issues Corsair has with Ryzen setups I'd find some other brand to go with for a Ryzen based build.
 

[Mark Kaine]

1 minute ago, qboIodp said:

so basically I should try to find a random video on yt to see what they use and if it works as it supposed to, prefer that?

No. It would probably be a better idea to ask here what RAM and motherboard would work well together with your CPU… People here are pretty knowledgeable about this stuff, unlike 99% of "techtubers".

[Master Disaster]

11 minutes ago, qboIodp said:

I was reading on another thread about the IF and some people said that it would be a waste of having 4000Mhz ram cause it wouldn't be able to achieve that because of the IF. Is that true, should I pick 3600 as they also said? 

Partially Incorrect.

 

What will happen with 4000 RAM in an 1800Mhz IF system is the bus would run at an asynchronous ratio. The IF runs at 1800Mhz (unless you manually OC it) however your 4000Mhz RAM would be running at 2000Mhz.

 

To work out the ratio we need to work out the GCF of the 2 numbers (the biggest number that will divide by both) and in this case that is 200.

 

1800 / 200 = 9

2000 / 200 = 10

So the IF bus would have to run at a 9:10 ratio, or another way, the RAM will be running 10 cycles on the bus for every 9 of the IF.

 

Now that said, there's no guarantee that your board or CPU will be OK running at a 9:10 ratio, that depends on how well you did on the silicon lottery but to say it will never work is not accurate either.

 

Edit - I assume the person who posted that probably meant that you wouldn't be able to push the IF to 2000Mhz to match the RAM which is 100% accurate. Some lucky people can get 1900Mhz on the IF but 2000Mhz is not possible in the vast najority of cases.

[Mark Kaine]

2 minutes ago, Beerzerker said:

Anything that's not Corsair that is.
Some Corsair sticks work fine with Ryzen but there is a real, definite trend for Corsair and Ryzen not working well together well established by all the threads we've seen that Corsair sticks in a Ryzen build having problems.

well and my luck is i have corsair, which has been recommended by many people, and ive been asking repeatedly too if there are any issues with this RAM for Ryzen CPUs…  (didnt ask on this forum tho, answers would have been probably different)

[Master Disaster]

2 minutes ago, Mark Kaine said:

well and my luck is i have corsair, which has been recommended by many people, and ive been asking repeatedly too if there are any issues with this RAM for Ryzen CPUs…  (didnt ask on this forum tho, answers would have been probably different)

I swear by Teamgroup RAM for Zen CPUs, it just seems to always work.

[qboIodp]

4 minutes ago, Mark Kaine said:

It would probably be a better idea to ask here what RAM and motherboard would work well together with your CPU

Anyone willing to recommend some sticks that they either are confident will work good with r9 5900x?

like maybe this one? https://www.crucial.com/memory/ddr4/bl2k8g36c16u4b

[Chris Pratt]

Some inaccurate info in this thread. Infinity fabric is not a replacement of front side bus. It's specific to Ryzen, because of its chipset based design. The fabric is the communication layer between the CCDs. It's similar in function to the role FSB played on Intel's first attempts at dual-core designs, where it was basically just two CPUs stuck together, with the FSB coordinating work between them, but that hasn't been a thing for a while.

 

Anyways. The IF clockspeed (FCLK) tends to cap between 1800-1900MHz on Zen 3. Some chips can go as high as 2000MHz, when the FCLK is OCed. For optimal performance on Ryzen, the FCLK should match the actual memory clockspeed (half the rated speed, because DDR is double data rate). That means the optimal RAM speed is twice what you can get your FCLK to. 3600MHz is recommended because it will at least go to 1800MHz, so anything higher may or may not be able to stay 1:1 with the FCLK, depending on your individual CPU. 

 

If you can't stay 1:1 (say you buy 4000MHz but the FCLK only goes to 1900MHz), then it switches to async mode and that can negatively impact performance up to 20% or more. However, if you do buy RAM that fast, you could downclock it to match whatever the FCLK can hit, and maybe roll that into tighter timings. It's still better to just get 3600MHz unless you're comfortable with RAM configuration, though.

 

As far as timings go, it's lower the better, but there's a point of diminishing returns. CL16 is pretty much perfect. You can get 3600MHz CL14, but it's stupidly more expensive, and the extra bit of perf doesn't even approach being worth it.

[Master Disaster]

8 minutes ago, Chris Pratt said:

Some inaccurate info in this thread. Infinity fabric is not a replacement of front side bus. It's specific to Ryzen, because of its chipset based design. The fabric is the communication layer between the CCDs. It's similar in function to the role FSB played on Intel's first attempts at dual-core designs, where it was basically just two CPUs stuck together, with the FSB coordinating work between them, but that hasn't been a thing for a while.

 

Anyways. The IF clockspeed (FCLK) tends to cap between 1800-1900MHz on Zen 3. Some chips can go as high as 2000MHz, when the FCLK is OCed. For optimal performance on Ryzen, the FCLK should match the actual memory clockspeed (half the rated speed, because DDR is double data rate). That means the optimal RAM speed is twice what you can get your FCLK to. 3600MHz is recommended because it will at least go to 1800MHz, so anything higher may or may not be able to stay 1:1 with the FCLK, depending on your individual CPU. 

 

If you can't stay 1:1 (say you buy 4000MHz but the FCLK only goes to 1900MHz), then it switches to async mode and that can negatively impact performance up to 20% or more. However, if you do buy RAM that fast, you could downclock it to match whatever the FCLK can hit, and maybe roll that into tighter timings. It's still better to just get 3600MHz unless you're comfortable with RAM configuration, though.

 

As far as timings go, it's lower the better, but there's a point of diminishing returns. CL16 is pretty much perfect. You can get 3600MHz CL14, but it's stupidly more expensive, and the extra bit of perf doesn't even approach being worth it.

I'm fully aware of the differences, I was just trying to keep it simple for explanation sakes.

 

Also I've never heard of a 20% hit from an async IF:RAM ratio.

[Chris Pratt]

8 minutes ago, Master Disaster said:

I'm fully aware of the differences, I was just trying to keep it simple for explanation sakes.

 

Also I've never heard of a 20% hit from an async IF:RAM ratio.

I can no longer find the source of the 20%, but Hardware Canucks measured an up to 15% latency penalty from async. They were looking at Zen 3, so it's possible the 20% I had heard was for earlier generations of Ryzen. This might be something that has been improved over time, or it may just be a YMMV thing. Either way, it's still significant.

 

[Beerzerker]

1 hour ago, Mark Kaine said:

well and my luck is i have corsair, which has been recommended by many people, and ive been asking repeatedly too if there are any issues with this RAM for Ryzen CPUs…  (didnt ask on this forum tho, answers would have been probably different)

Annnnnnd let me guess..... Vengeance series sticks?

[Mark Kaine]

2 hours ago, Beerzerker said:

Annnnnnd let me guess..... Vengeance series sticks?

Of course!  Funny thing i could have bought any other, but no, thats what has been recommended by internet "experts" repeatedly "cant go wrong with those…"  ʕ•ٹ•ʔ

[brob]

Crucial and G.Skill have decent and easy to use motherboard QVL. Corsair has QVL data but I've found it difficult to use and generally not worth the effort.