CPU VCore and Memory compatibility

kidanime3d · Dec 11, 2013

The more I read on RAM and CPUs, the more conflicting information I seem to come across.

1. Does Ram have to be +/- 0.5 volts from the CPU VCore to work? Does that mean if stock voltage on the i7-4770k is 1.1V(I know this differs slightly from chip and board combo), it doesn't need overclocking for this

http://www.scan.co.uk/products/16gb-(2x8gb)-corsair-ddr3-vengeance-pro-series-silver-pc3-17066-(2133)-non-ecc-unbuffered-cas-11-11-

but will require overclocking for this

http://www.amazon.co.uk/Skill-PC3-19200-2400MHz-Gaming-Memory/dp/B007V9PZFI/ref=sr_1_1?ie=UTF8&qid=1386763063&sr=8-1&keywords=trident+x

Answers:
Yes, +/- 0.5 is necessary due to MC requirement.
XMP will alter the CPU voltage accordingly so the RAM can run at required speeds, how much depends on CPU.

2. If the above holds true, does that mean you will not damage the MC on the CPU if keep the temps down?

Answers:
Yes

3. Intel recommend 1.5V +/- 5% based on JEDEC and don't officially support voltages above 1.5, however after reading dumps of chats with Intel support it seems you can only void warranty if there are visible burn marks from high voltage, has anyone had experiences to contradict this?

Answers:
What intel doesn't know, won't hurt them, though keeping with number 2 shouldn't cause any issues.

HEXiT · Dec 11, 2013

that ram is a waste for that cpu. the cpu handles up to 1866 natively so anything faster is just for benchmarks and has no real world performance gains. better to get slower 1866 with lower cas latency.

yes the ram has to be within .5v of the cpu or you can damage the mmu. so try for 1.35v ram. that way you will be within spec even when your cpu down volts if your running energy savings.

kidanime3d · Dec 11, 2013

HEXiT :

Thanks for your response you answered the first part of question one.

I would like to stress this is not a help to buy RAM question but a technical question.

How much does the voltage differ when the i7-4770k goes into energy saving? Is this BIOS, OS level?

Supahos · Dec 11, 2013

ram doesn't have to be any ratio to vcore it doesn't matter, if you're going to buy the 8gb 2400 MHz tridents look for the CL9 ones, they actually do have better performance and its the only kit on the market I've seen for any kind of reasonable prices that can run that way by simply enabling xmp. Running at 1.65 v won't hurt anything or require you to run a vcore of any specific number.

kidanime3d · Dec 11, 2013

Supahos :

Based on what source of information?? There seems to be a consensus around +/- 0.5V from memory voltage to CPU voltage.

HEXiT · Dec 11, 2013

intels own recommendation is 1.5v max mate for the haswell and ivy parts. always err on the side of caution because its not my pc that could potentially fry. if intel say 1.5 then thats good enough for me.

kidanime3d · Dec 11, 2013

HEXiT :

I already knew that hence third question.

I will update my question to reflect that.

Effective cooling can remove any heat problems, I will be using the Noctua DH-14

Supahos · Dec 11, 2013

You dont' have to up the cpu voltage in order to run any specific dram voltage, are you sure you don't have it confused with intel "recommending" only going to 1.55v?

kidanime3d · Dec 11, 2013

Supahos :

No, sorry, I was referring to the voltage of the Memory Controller on the CPU needing to be within +/- 0.5v from that of DRAM.

Supahos · Dec 11, 2013

Oh when you set XMP it will take care of that part itself usually, thought u meant vcore. Raising VCCSA won't hurt temps much, and with that cooler should be more than enough to dissipate the heat.

kidanime3d · Dec 11, 2013

Supahos :

I see.

So let say I have the 1.1v 4770k, when loading the XMP for the DRAM, if the voltage for the DRAM is outside the 0.5V, the DRAM will not reach its' full potential, is that correct? or will it stay at motherboard default?

Supahos · Dec 11, 2013

Once you enable xmp it will adjust all things necessary in order to get it to work at the speed. I suspect this is why some have actually reported heat increase with faster memory and some report none. Maybe some already had the voltages inside of that window and others didn't? I do know if you buy better ram (like say gskill tridents) they all have some OC room left to be found, and you can either use it to go faster, lower timings, or option 3, which is drop the dram voltage. Someone on their forms a few weeks back managed to get 32gb of 2400 tridents fully stable at 1.53v.

kidanime3d · Dec 11, 2013

Supahos :

That makes sense, thank you for the further clarification.

So 1.1v CPU with 1.5V DRAM will not require an CPU overclock while a 1.65V will, that's good to know

Supahos · Dec 11, 2013

well adding voltage and an OC aren't quiet the same thing. Never buy any ram over 1.5v that is 1866 or lower speed. and for 2133 most good ram will run at 1.6 or lower, and if you enthusiast ram (1.65 low timing ram) you should be able to get 1.6v to work pretty easily.

kidanime3d · Dec 11, 2013

Supahos :

I generally associate a voltage increase with a OC although it is not 100% accurate.

Supahos · Dec 11, 2013

overclock only technically referrers to actually clocking something faster than it was before voltage does nothing but affect stability.

HEXiT · Dec 11, 2013

seriously? id love to see your evidence that says running 2400 speed ram is any better than 1866 on an intel i5 system coz as far as i know there is no performance gains other than maybe 1-2%. yes in benches you will see higher numbers but in the real world applications the increase in speed accounts for nothing. other than a dent in the wallet.
all the benches toms has put up about ram showing that 1600 ddr3 is within 1-2% of ddr3 2400 due to the slower rams lower latencies and the limits of the intel cpu's MMU please goo look em up... yet the ddr3 2400 is rated at 33% faster in raw mhz and so much more expensive.
my own experience tells me the same.

http://www.anandtech.com/show/7364/memory-scaling-on-haswell/3 proves my point. they test everything from 1333 up to 3000 but 1s the native speed of the cpu's mmu is reached there is no perfomance gains. with the 1 exemption being win rar that uses cpu and memory in a very specific way.

kidanime3d · Dec 11, 2013

HEXiT :

This was a technical question requiring a technical response which has kindly been given.

I see no reason to continue this discussion unless you are going to answer the question I directed at you earlier which is "what is the difference in voltage during energy saving? Is this bios or os level?"

HEXiT · Dec 11, 2013

its hardware level bios controlled. should be depending on your cpu sample between 0.8 and 0.9v for the basic idle. the memory doesnt get undervolted it stays at what ever its set at either manually or with the xmp profiles.

btw my question wasnt aimed at you OP it was aimed at supahos.

kidanime3d · Dec 12, 2013

HEXiT :

That is really good to know, thank you.

Just spoke to intel, They said "Idle Voltage on the i7 4770k is 0.6-0.7, and it has a maximum of 1.3 @ stock."

The VTT of the IMC does need to be within +/- 0.5 so energy saving may need to be turned off.

You didn't quote supahos so it was very unclear.

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