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Ram over-voltage req. at default speed: why? is it safe?

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March 12, 2007 1:51:09 PM

Hi,

I got a Core2 dup E6600 on an ASUS P5B-Deluxe
I also have 2 sticks of 1GB ddr2 667 (Kingston KVR667D2N5)

When I overclock my cpu and set the bus to 333 (1333Mhz), and set the memory at 1:1 (so 666Mhz), the system won't boot, black screen. However with OCZ memory modules it works perfect, so I started to suspect the Kingston memory.

After a lot of testing, I managed to make the system work with those Kingston stick... by over-volting the DDR to 2.1V even they are working at 666Mhz (which is their spec).


The system seems stable, I did some prime95 torture tests successfully... now I'm wondering if it is safe to run those Kingston DDR at 2.1V as the memory chips get pretty hot? I don't have any memory heatsink on hand

Also, any idea why I need to increase the voltage of the DDR when they're not overclocked?

Thanks,

David.
March 12, 2007 10:44:15 PM

Quote:
...

Also, any idea why I need to increase the voltage of the DDR when they're not overclocked?
....

1) They may have been sold as a manufacturer-sanctioned overclock, so their spec may require a voltage higher than 1.8V to work at DDR2-667.
2) If not, and assuming you set the memory settings to "auto" or entered correct ones manually, it sounds like they are defective and should be replaced under warranty.
March 13, 2007 7:23:28 AM

Well, the rams are specified to run at 667Mhz at 1.8V. And they are not defective neither (got 12 sticks around, any combination of 2 or 4 give the same result).

Now if the cpu is not overclocked and I set the memory speed to 667, it works fine at default voltage! The memory sur-voltage is necessary only if I overclock the cpu... Is it possible that higher speed FSB causes some interferences in the memory modules and then require an increased voltage to increase signal strength?

Well, it's working well at 2.1V... but I'm afraid about how long the ram will live as they are getting quite hot (but no error... yet)
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March 13, 2007 7:49:12 PM

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Now if the cpu is not overclocked and I set the memory speed to 667, it works fine at default voltage! The memory sur-voltage is necessary only if I overclock the cpu......

Aha! Some BIOSes deal with memory vs FSB speed settings in a confusing way. Rather than treating the 667 (for example) as an absolute number, they look at it as a ratio relative to the FSB speed. For non-OC conditions, this is fine, as 266:667 converted into a 2:5 FSB:RAM ratio still gives DDR2-667 speed. However, if you OC the FSB, but the ratio doesn't change, this can cause problems. If the FSB is boosted to 333, the RAM will then run at 333 x 5/2 = DDR2-833 speed.

This would explain your results, as the Kingston ValueRAM is not premium RAM, so wouldn't be expected to work much faster than DDR2-667 under normal conditions. The OCZ modules presumably are premium RAM, and so will work at significantly faster speeds than their rated speed.
March 13, 2007 8:44:29 PM

Quote:
333 x 5/2 = DDR2-833 speed.

Quote:
When I overclock my cpu and set the bus to 333 (1333Mhz), and set the memory at 1:1 (so 666Mhz), the system won't boot

I think he has his ratio's right
On that note, I personally have no idea what's going on. maybe try running memtest86. see if you get any errors with that.
Good luck
March 14, 2007 7:38:39 AM

The ratio was fine, the ram was really working at 667, not 833, I used 1:1 ratio instead of 5:4. By the way those rams won't go much higher than 667 whatever the voltage. So I could definetly not boot at 833.

I really suspect some interferences in the memory modules with higher fsb.
March 14, 2007 8:07:44 PM

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I really suspect some interferences in the memory modules with higher fsb.

Since the memory modules are not connected to the FSB, I don't see how that could be the case.
March 14, 2007 8:09:07 PM

Quote:
.... By the way those rams won't go much higher than 667 whatever the voltage. So I could definetly not boot at 833.....

But that's what you said happened: the kingston's didn't boot, but the OCZs (which can run faster) did boot.
March 14, 2007 9:09:29 PM

Well, it is working if I increase the voltage to 2.1V, not at default voltage. if I try to run the ram faster than what it is supposed to work, it won't work at all, whatever is the voltage (I didn't try much, but it won't start for sure even at 750Mhz).

For the interferences, I know the ram speed and fsb are not related, but it could be possible that higher fsb causes stronger noise or interferences in the memory. Even the memory and fsb are not "connected" circuits on the motherboard are connected. I can see the same problem with 12 sticks of those kingston rams over 6 moderboards (all P5B-Deluxe), so it's not a defective mb or ram stick. And I tested this with Core2 duo E6600 and E6400.

btw, OCZ is guaranteed at 2.1V, so it might be why they work as well... plus they are 800Mhz rams (and I use them only at 667Mhz). No doubt they are better

The fact was just that Kingston at 667 with bus at 266 and fsb:ram ratio of 4:5 works good at default voltage (1.8V), but those same rams at 666 with bus at 333Mhz and fsb:ram ratio of 1:1 is a no go unless I increase ram voltag to 2.1V
!