Question Confused about memory - MT’s and Mhz, XMP - PC wont boot with XMP enabled

[ItzEvolv]

Hi, I have searched for a bit but the more I look up on this the more confused I end up being.

I build a new PC, forgot to check RAM speed. Everything worked fine. I checked taskmanager yesterday and saw that my memory runs on 4000MHz.

Now, my RAM should be capable of 6000MT/s. I enabled XMP in my BIOS, which automatically was set on 6000MHz. I saved, rebooted, PC took a long time to start and end up in a American Megatrends screen telling me that it stopped booing because the system is unstable.

At first I thought that mt/s and mhz were the same, but after some searching online I found that the mhz should be half of the mt/s.
That still does not add up for me, as my memory runs on 4000mhz stock without XMP enabled and 2x4000 would be 8000mt/s then?

I think I’m kind of confused and don’t understand how this works.

My RAM kit: Kingston Fury Beast KF560C36BBEK2-32
CPU: 13600KF
Motherboard: Asus Prime Z790-A WiFi

Any help would be appreciated.

 

[Lutfij]

When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

The speed reported in Task Manager is the current ram's speed.

 

[ItzEvolv]

When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

The speed reported in Task Manager is the current ram's speed.

Thanks for your reply but I’m asking general knowledge about MT/s, MHz and XMP profiles for RAM. I have listed the specs of my motherboard, RAM and CPU at the bottom of my post. First I’d like to know if I’m misunderstanding anything about what I tried to do. If necessary, I will obviously take the time to look up my BIOS revision and what not. But I feel like I’m just missing something about how XMP and RAM speeds work.

I’m just trying to get a basic understanding of if what I did was correct or just simply wrong. I don’t think people need to know my monitor specs for this.

 

[Deleted member 2969713]

At first I thought that mt/s and mhz were the same, but after some searching online I found that the mhz should be half of the mt/s.
That still does not add up for me, as my memory runs on 4000mhz stock without XMP enabled and 2x4000 would be 8000mt/s then?

You can thank the marketers of RAM sticks for this confusion. Generally, when a stick is marketed at a given MHz, what they really mean is MT/s. BIOS interfaces can also misuse MHz, presumably in an attempt to avoid confusing customers not in the know, so that they aren't all like, "my RAM said it could go to 4000 MHz and it's only at 2000, what gives????"

RAM sticks used to be SDR, single data rate, and at that time the MT/s matched the frequency. But when memory was changed to DDR, double data rate, the MT/s became double the frequency. See https://www.cgdirector.com/mts-vs-mhz/

As for why your system wasn't working with XMP enabled, I'm not sure. I looked it up and technically your CPU is only rated to support 5600 MT/s on DDR5, so maybe that could be the cause?

 

[ItzEvolv]

You can thank the marketers of RAM sticks for this confusion. Generally, when a stick is marketed at a given MHz, what they really mean is MT/s. BIOS interfaces can also misuse MHz, presumably in an attempt to avoid confusing customers not in the know, so that they aren't all like, "my RAM said it could go to 4000 MHz and it's only at 2000, what gives????"

RAM sticks used to be SDR, single data rate, and at that time the MT/s matched the frequency. But when memory was changed to DDR, double data rate, the MT/s became double the frequency. See https://www.cgdirector.com/mts-vs-mhz/

Exactly, but that does not add up for my RAM kit then. 6000MT/s, and it won’t boot with XMP enabled on 6000MHz.

Task manager and BIOS says 4000Mhz on stock “auto” settings, but 4000x2=8000. So that’s not the advertised MT/s.

So that makes that I’m even more confused. Is my kit 6000MT/s or Mhz? And when enabling XMP, what would the logical speed be to set up if default is 4000Mhz on Auto?

 

[Deleted member 2969713]

Task manager and BIOS are both using MHz in the common vernacular sense, meaning actually MT/s. It's definitely not running at 8000 MT/s on stock.

The RAM kit is 6000 MT/s, or 6000 MHz in common vernacular, but really actually 3000 MHz. To Kingston's credit, they seem to be actually using MT/s in their marketing and product information for those sticks rather than "MHz".

As per my edit to my first post, the CPU technically only supports 5600 MT/s, so you might want to try limiting the RAM speed to that and see if it works.

 

[ItzEvolv]

Task manager and BIOS are both using MHz in the common vernacular sense, meaning actually MT/s. It's definitely not running at 8000 MT/s on stock.

The RAM kit is 6000 MT/s, or 6000 MHz in common vernacular, but really actually 3000 MHz. As per my edit to my first post, the CPU technically only supports 5600 MT/s, so you might want to try limiting the RAM speed to that and see if it works.

Aha, thanks! Didn’t know that the CPU had a speed limitation. I think I’m starting to get it.

Any idea why it would revert to 4000Mhz on auto than? That’s a thing I still don’t understand. Could it possibly be that a RAM kit runs faster or more stable on a lower frequency that is well within spec?
Does the frequency also affect the timings?

 

[Deleted member 2969713]

Aha, thanks! Didn’t know that the CPU had a speed limitation. I think I’m starting to get it.

That's its officially supported limit for memory speed. It's possible to go beyond it, but to do so is considered overclocking and is thus not guaranteed by Intel to work. If the system is unstable beyond that limit, then keeping at or below that limit might fix the problem.

Any idea why it would revert to 4000Mhz on auto than? That’s a thing I still don’t understand. Could it possibly be that a RAM kit runs faster or more stable on a lower frequency that is well within spec?
Does the frequency also affect the timings?

I won't pretend to be an expert on memory, so someone else might be able to better answer those questions. In particular, RAM timings are a bit of black box for me. As for why it starts off at 4000 MHz (read: MT/s), I believe that's because that's simply its stock clock, and any higher is technically an overclock, albeit an officially supported one. It certainly won't be faster at a lower frequency, but more stable may be a possibility.

 

[SkyNetRising]

Any idea why it would revert to 4000Mhz on auto than? That’s a thing I still don’t understand.
Does the frequency also affect the timings?

Can you show screenshots from CPU-Z - memory and spd sections?
(upload to imgur.com and post link)

Tas Manager is not a reliable tool for ram frequency detection.
It can show default ram speed, xmp speed, current speed. And you can't know which.
CPU-Z - is more precise.

And of course, frequency and timings depend on each other. They are linked.