PC Memory 101: Understanding Frequency and Timings

TJ Hooker

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  • Intel’s LGA 1151 processors have memory controllers that are stable well beyond DDR4-3600, but the firm locks out high ratios to prevent them from being used on non-K-series processors. [...]
  • Intel also figured out a way to get non-Z-series chipsets to instruct any CPU (even a K-series) to lock out higher ratios. The only easy way to exceed DDR4-2666 on any of this hardware is to use a Z-series (Z390, Z370, Z270) chipset with a K-series Core i5 or higher processor.
This is wrong. It only depends on whether you have a Z series motherboard, not whether you have a K series CPU.
 
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Ariur

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The article claims Intel locks i3 to 2400 MHz and all other non-K CPU to 2666 MHz. This is false information. As long as you have Z-series motherboard, you can set any RAM speed for i3 and non-K processors. And no "workarounds too lengthy to describe" are required. You go to BIOS, set base RAM frequency and multiplier (+adjust voltage, if necessary), reboot, and you are done.

I'm writing right now from a PC with i3-8100 running with DDR4-2933. Which, according to the author of this article, isn't even possible.

It seems a lot of people are still confused by DDR4-2400/DDR4-2666 memory support Intel (and most shops) list in CPU specifications. These are just recommended RAM frequencies, not maximum supported frequencies.
 
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TJ Hooker

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We were not able to set any ratios higher than 12x100 (xDDR) or 9x133 (xDDR) on the Core i3-8350K. And the processor knows whether you're using a 100 or 133 memory controller frequency, so 12x133 wasn't even possible. To get the memory to DDR4-3200, we had to reduce the CPU multiplier, then increase the BLCK to 133 MHz. And that's too much information to put into an article like this.
What motherboard? I had an i3 6100 + Z170 and I could run 2800 MHz just fine.
 

Crashman

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I tested the 8350K and found that I had to overclock BCLK to reach higher data rates. I don't remember the board...could that have been on a special unlocked board?

I'm just going to delete my comments and get back to you in about 10 minutes with a retest.

Edit: I think I lent the CPU to another tester. I did find this reference to the Z370 test I did, in which I squeezed the tears of of the BCLK in order to get the memory to DDR4-3504 (probably 146 MHz using the 12x100 ratio and the CPU cranked down to its lowest multiplier).
 
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Ariur

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I tested the 8350K and found that I had to overclock BCLK to reach higher data rates. I don't remember the board...could that have been on a special unlocked board?

I'm just going to delete my comments and get back to you in about 10 minutes with a retest.

Edit: I think I lent the CPU to another tester. I did find this reference to the Z370 test I did, in which I squeezed the tears of of the BCLK in order to get the memory to DDR4-3504 (probably 146 MHz using the 12x100 ratio and the CPU cranked down to its lowest multiplier).
Perhaps there was some motherboard firmware issue, or you had some rare motherboard edition with limited RAM speed support? Using RAM speed above 2400 is certainly possible for i3 processors (both K and non-K) with Z370 motherboards. And no, it doesn't require changing base clock (BCLK).

This information is easily available online. Here is a blog post by MSI showing performance of i3-8350K depending on RAM speed:

https://www.msi.com/blog/Unlock_more_FPS_by_optimizing_DDR4_performance

They tested all RAM frequencies up to 3200, just by changing RAM speed multiplier.

 
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Crashman

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Perhaps there was some motherboard firmware issue, or you had some rare motherboard edition with limited RAM speed support? Using RAM speed above 2400 is certainly possible for i3 processors (both K and non-K) with Z370 motherboards. And no, it doesn't require changing base clock (BCLK).

This information is easily available online. Here is a blog post by MSI showing performance of i3-8350K depending on RAM speed:

https://www.msi.com/blog/Unlock_more_FPS_by_optimizing_DDR4_performance

They tested all RAM frequencies up to 3200, just by changing RAM speed multiplier.

That doesn't show me BCLK though, so I still don't know that the i3-8350K ever exceeded 2400 at 100MHz BCLK. I only know that my test required overclocking BCLK to reach past DDR4-2400.

I found the information from the review, where I was forced to O/C the BCLK to get a higher data rate. Could Intel have locked down the memory ratios on the 8350K when it unlocked the CPU core ratios...just because it wanted to?

"As the chipset would indicate, only the Z-series board was overclock-capable, and base clock manipulation was the only way to overclock the RAM past DDR4-2400 on the tested Core i3-8350K. The CPU did surprisingly well, pushing our DDR4-3200 to DDR4-3504 despite the CPU's ostensible limits."
https://www.tomshardware.com/reviews/h370-b360-budget-coffee-lake-motherboard-roundup,5548-6.html
 
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Ariur

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That doesn't show me BCLK though, so I still don't know that the i3-8350K ever exceeded 2400 at 100MHz BCLK. I only know that my test required overclocking BCLK to reach past DDR4-2400.
If you actually bothered to check the MSI article I linked you would know they had BCLK set to 100MHz, as can be clearly seen in screenshots. The big red rectangle in the center, can't be that difficult to notice, even for a "senior editor" from Tom's Hardware. :unsure:



I have also posted above a screenshot from my own PC, i3-8100, running with DDR4-2933, and no, I didn't change BCLK. It's set to 100MHz. Because guess what? All i3 CPUs support any RAM speeds, as long as they are plugged into Z-series motherboards. The only limits are imposed by motherboards, for z370 chipsets these limits are usually at or above 4,000MHz. All this information is available everywhere online, and was available for years.
 
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Crashman

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If you actually bothered to check the MSI article I linked you would know they had BCLK set to 100MHz, as can be clearly seen in screenshots. The big red rectangle in the center, can't be that difficult to notice, even for a "senior editor" from Tom's Hardware. :unsure:



I have also posted above a screenshot from my own PC, i3-8100, running with DDR4-2933, and no, I didn't change BCLK. It's set to 100MHz. Because guess what? All i3 CPUs support any RAM speeds, as long as they are plugged into Z-series motherboards. The only limits are imposed by motherboards, for z370 chipsets these limits are usually at or above 4,000MHz. All this information is available everywhere online, and was available for years.
No. The Z370 board I used as the baseline for the H370 test did NOT support higher memory multipliers. I did not lie when I wrote that over a year ago. I just found the test note that I had to use 146 MHz BCLK to hit DDR4-3504:
36

Beyond the purely accurate thing that I wrote at the time, I'm left to guess that the higher multipliers could be set but the resulting data rate was still DDR4-2400. And the reason I'm left to guess is that I no longer have the CPU. Which is why I spent 45 minutes looking for the CPU before realizing that I sent it to our CPU cooling tester. Maybe I should have taken more notes, but I didn't foresee this conversation happening a year later.
 
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Understanding memory is more than just about capacity and speed. We’ll walk you through what you need to know about timings/latency, ranks and more.

PC Memory 101: Understanding Frequency and Timings : Read more
I'm not the smartest person around, but I figured a story about ...
"Back to the Basics"
...would explain the basics.
There is a nifty photo highlighting CL16-16-16-36.
That is 4 numbers.
The following paragraph went on to explain CAS, tRCD, tRP, tRAS, CMD.
That is 5 numbers.
It also used 10ns which also doesn't seem relate to that nifty picture either.
This may be the last computer I ever build, my last one was an Ivy Bridge, and at nearly 70 years of age I do understand reality. I want to not only game some but edit RAW photos and 4K video. I understand how much RAM I need, just not what kind for a RYZEN 5000 series.
I'm just trying to learn the basics... maybe it is just because I am old, but your article was more confusing than helpful.
Please excuse my ignorance, I'm just trying to build a computer before I die and considering how hard it is to get the new hardware I may not succeed
 

Crashman

Polypheme
Former Staff
I'm not the smartest person around, but I figured a story about ...
"Back to the Basics"
...would explain the basics.
There is a nifty photo highlighting CL16-16-16-36.
That is 4 numbers.
The following paragraph went on to explain CAS, tRCD, tRP, tRAS, CMD.
That is 5 numbers.
It also used 10ns which also doesn't seem relate to that nifty picture either.
This may be the last computer I ever build, my last one was an Ivy Bridge, and at nearly 70 years of age I do understand reality. I want to not only game some but edit RAW photos and 4K video. I understand how much RAM I need, just not what kind for a RYZEN 5000 series.
I'm just trying to learn the basics... maybe it is just because I am old, but your article was more confusing than helpful.
Please excuse my ignorance, I'm just trying to build a computer before I die and considering how hard it is to get the new hardware I may not succeed
The first four are specified by the module. The fifth, command rate, is usually picked by the board at 1T or 2T depending on frequency and the number of ranks deployed per channel. Manually selecting a 1T command rate for quicker response times is often possible, but that falls under manual tuning, with the tradeoff being possible instability.
Feel free to view this video for an even faster and simpler explanation of the first four timings.
 
With 10th gen, if you are using a B,H, or Q series motherboard, ram speed is limited to the following
i5 and below - 2666mhz
i7 and i7 - 2933mhz
Being a K series CPU does not change this.

I had an i3 8100 on H310 and indeed, ram could not run over 2666mhz. If you can run it over this, it is an exception.
 
Nov 28, 2020
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The first four are specified by the module. The fifth, command rate, is usually picked by the board at 1T or 2T depending on frequency and the number of ranks deployed per channel. Manually selecting a 1T command rate for quicker response times is often possible, but that falls under manual tuning, with the tradeoff being possible instability.
Feel free to view this video for an even faster and simpler explanation of the first four timings.
Thank you.
The video was a lot of help, as was your explanation of the command rate.
Still a lot to learn, but that was helpful.
 

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