Understanding x99 memory

digitaldreams

digitaldreams

digitaldreams

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Joined
5 Jul 2007
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510
Hi folks

I used to understand the old Intel systems re bus and ram speeds but are a little lost with x99. My current setup is below (gleamed from CPUz).

i7-5820k 3.3GHz, multiplier 12-34
Bus speed 99.94MHz
Northbridge 1199MHz

Dram frequency 1066MHz, CL15-15-15-36
SPD - 1066MHz 15-15-15-36 1.2v, 1200MHz 14-16-16-31 1.2v, 1333MHz 14-16-16-35 1.35v

My motherboard manual suggests that anything above DDR4 2133 is 'overclocking'. My current ram reports itself as 2133 yet the part number is 2400C14

Thoughts....

1...'2400' is 1200MHz doubled ('DDR') hence 2133 is 1066MHz ?
2...This is CL14 ram so why does the spd set CL15 at the slower 1066MHz ?
3...Do CL timings notably affect performance like they did on the old systems ?, is it worth forcing CL14 instead of the current CL15 ?.
4...To run this ram at 1333MHz (top spd setting) do I need to up the bus or northbridge frequency ?, yes I see a voltage jump too. What about reliability if I do ??. Performance is great but reliability is much more important to me. I guess there is no way of running faster ram without at least 'overclocking' the bus frequencies (as apposed to simply increasing multipliers to run say DDR4-3600/3866 sticks)

Regards
 
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I'm not entirely clear on it either, but my experience was (X99 ASUS Deluxe) -

Memory advertised speed 2666
Installed and it defaulted to 2133
Enabled XMP (and therefore overclocking) and the it clocked the memory at 2800, when I tried to force is to 2666 the system became very unstable. Left it at 2800.

I believe the key is XMP and everything just falls in place - memory overclock and the base cpu clock.
 
All memory is JEDEC spec which for DDR4 the default operating frequency is 2133. Anything above this is overclocking.

Speeds above this are binned by the memory vendors and then programmed on to the modules on spare SPD tables.

When the XMP profile is applied, all this does is auto adjust the BIOS values to the frequency and primary timings the memory was binned at by the vendor. In this case 2400.

That's all you really need to know.

faxfan said:
I'm not entirely clear on it either, but my experience was (X99 ASUS Deluxe) -

Memory advertised speed 2666
Installed and it defaulted to 2133
Enabled XMP (and therefore overclocking) and the it clocked the memory at 2800, when I tried to force is to 2666 the system became very unstable. Left it at 2800.

I believe the key is XMP and everything just falls in place - memory overclock and the base cpu clock.
Click to expand...



A lot of the ratios on X99 are still fairly broken TBH. Beyond 2400 the only one that's not slightly hit and miss is 3200. Most in between this can require further tuning from the user.
 
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How do you enable XMP?
I have a Gigabyte x99m MB with 4x8gb Team Group memory. I have managed to overclock my i75930 to 46x multiplier but not really tried to push the memory as I have not really got a clue which is the best way to do it.
 
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