How does CPU overclocking affect memory?

[Cs342]

I have noticed that when I change the CPU multiplier on my 2600K the RAM frequency automatically changes. Why is this and what effect does it have on performance?

[Giac]

Cs342, on 17 Jun 2013 - 12:10 PM, said:

I have noticed that when I change the CPU multiplier on my 2600K the RAM frequency automatically changes. Why is this and what effect does it have on performance?

That shouldn't happen. Changing the CPU multiplier should have no effect on RAM freq. The only time you can change your RAM speed indirectly is by changing the BUS freq....which you can't really do on Z68/Z77. Do you have X.M.P. enabled in your BIOS?

[Cs342]

That shouldn't happen. Changing the CPU multiplier should have no effect on RAM freq. The only time you can change your RAM speed indirectly is by changing the BUS freq....which you can't really do on Z68/Z77. Do you have X.M.P. enabled in your BIOS?

I just set everything to auto. It says 1333MHz when I leave CPU frequency at auto and mem. frequency at auto but when I bump the clock speed up the RAM changes to 1600MHz

[Cs342]

Also I'm writing a paper on overclocking so would like to know how CPU overclocking affects memory. If I recall correctly, RAM used to be vital to overclocking until Sandy Bridge.

[samuel]

what is xmp? use manual mode, we are enthusiasts!  ^_^

[Giac]

Also I'm writing a paper on overclocking so would like to know how CPU overclocking affects memory. If I recall correctly, RAM used to be vital to overclocking until Sandy Bridge.

Yes correct. Back in the C2D days the only way to overclock was through the FSB (Front Side Bus). Changing this value would not only overclock the CPU but also the RAM. To mitigate this you could select specific ram dividers. So say while the bus speed for the CPU is 133Mhz, the Ram freq would be 100Mhz.

 

Really odd that your ram speed goes from 1333Mhz to 1600 on its own accord....Have you tried manually setting your timings + speed to 1600Mhz and seeing what happens? Does the BIOS up the speed to 1866?

[asusfan]

I have noticed that when I change the CPU multiplier on my 2600K the RAM frequency automatically changes. Why is this and what effect does it have on performance?

The only reason i can see it doing this is if your using o/c software, it will change both the cpu and memory. well thats what the Asus AI Suite II software does.

 

If your just doing it manually then i don't know what unless some kind of software automatically is adjusting the ram without you knowing.

[Cs342]

I switched to XMP and the memory speeds no longer change by themselves. Thanks for the help!

Can someone please explain the role of RAM in Sandy Bridge/Ivy Bridge/Haswell overclocking?

[Giac]

I switched to XMP and the memory speeds no longer change by themselves. Thanks for the help!

Can someone please explain the role of RAM in Sandy Bridge/Ivy Bridge/Haswell overclocking?

No problem bro!

 

Normally RAM should play no role in overclocking for Sandy/Ivy. The only thing to keep in mind is that as you overclock, maintaining a high ram frequency (say 2100Mhz) will be more difficult and may involve bumping the (RAM) voltage and/or lowering your RAM speeds under their certified frequency. Populating all the DIMMs has a similar effect.

 

Note that this is true for almost all sockets, including AM2/AM3/AM3+

 

Hope this clears up some of the questions you have. Again I have no idea why your MB decided to act in such a way. My best guess would be a bug in the BIOS?

[DavePC]

I have noticed that when I change the CPU multiplier on my 2600K the RAM frequency automatically changes. Why is this and what effect does it have on performance?

 

Generally overclocking your CPU has no effects. However, on Haswell it supports higher memory speeds. When you start to overclock your CPU, it stresses out the main CPU, and there is less power for the memory controller. Therefore, you may not have support for very high speed memory such as DDR3-2400+.

[Cs342]

So in the old days if you raised the CPU clock speed you would also have to raise memory speeds? And with Sandy Bridge and above that is no longer the case?

[Giac]

So in the old days if you raised the CPU clock speed you would also have to raise memory speeds? And with Sandy Bridge and above that is no longer the case?

Correct :)

 

However back in the day you could still get processors with unlocked multipliers. My AMD Phenom II 955 BE for example...

[Cs342]

Correct :)

 

However back in the day you could still get processors with unlocked multipliers. My AMD Phenom II 955 BE for example...

I thought the old overclocking technique revolved around changing the base clock?

[Giac]

I thought the old overclocking technique revolved around changing the base clock?

IIRC at the time the only intel chips that had unlocked multipliers were the extreme edition processors, and those were expensive. Thats why overclocking via fsb was common practicse.

 

EDIT: this http://www.anandtech.com/show/2045/18

[Cs342]

IIRC at the time the only intel chips that had unlocked multipliers were the extreme edition processors, and those were expensive. Thats why overclocking via fsb was common practicse.

 

EDIT: this http://www.anandtech.com/show/2045/18

If you could overclock the FSB then why would you even need the multiplier? The CPU would hit a thermal limit before the FSB was "used up".

[Giac]

If you could overclock the FSB then why would you even need the multiplier? The CPU would hit a thermal limit before the FSB was "used up".

Using the multiplier was typically easier because you didn't have to worry so much about overclocking the rest of your components.