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Mixing RAM of Different Latency & Size

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February 23, 2010 6:44:37 PM

Hi,

I'm considering adding memory to my current rig, and was hoping someone here can help me out. I've got a Asus P7P55D Pro mobo with a 4GB of Kingston ValueRAM DDR3-1333 (PC3-10600) RAM. It's got a 9-9-9-27 latency and uses 1.5 volts.

Am I facing any potential issues if I dual channel my current memory with
1) memory of different size (pairing my pair of 2GB with a pair of 4GB)?
2) memory of different brand series (Kingston ValueRam vs Kingston HyperX)?
3) memory of different latency (one of the sticks im looking at has a 7-7-7-21 latency)?

I tried looking up a lot of this stuff. From what I understand, pairing memory of different size shouldn't be an issue, but it was rather difficult to find anything on brand series and latency (at least anything consistent).

Thanks!
February 23, 2010 6:49:17 PM

the only thing i can see being an issue is latency.. they will be hard to configure in the bios. so regardless they will probably all run at the same latency wich could cause problems if that specific ram is not able to run that latency...

i would buy ram with the same speed and latency rating.. (as usually recomended by the mobo manufacurer)
February 23, 2010 9:06:20 PM

You will see a significant performance difference. It would be like putting a standard engine in a ferrari. Basically you wouldn't like it
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a c 149 } Memory
February 23, 2010 9:38:47 PM

You should have no problems. The memory will default to the speed and latency of the slowest sticks.

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a b } Memory
February 23, 2010 11:32:17 PM
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When you mix different types of RAM, you may not understand all that entails this task. Like the Ferrari example above, sure the engine fits the chassis, but you're not getting the same performance.

To be more clear, latency, timing, and voltage are all necessary considerations. Dark mentioned that it is recommended to use matching RAM. This is because when mixing, the physical memory will be recognized, but the total RAM will perform at the highest latency.

If you have to mix the RAM, make sure that all of the RAM can operate at the highest latency, the slowest timing, and the highest voltage required. You may get lucky and find nothing will happen if your BIOS settings are left set at "auto", or you may get unlucky and have, at minimum, at computer that doesn't boot properly.
February 24, 2010 3:44:35 PM

Thanks for the help!

I figured, mixing different latency would be an issue, and that mixing different speeds, at the very best, would be pointless since I'd be bottlenecked by the slowest speed.

As for mixing different sizes, I checked my Asus P7P55D manual, and it mentions I CAN install varying memory szies in channels A & B. It does say that excess memory from the higher sized channel is mapped for single channel operation...

Quote:
You may install varying memory sizes in Channel A and Channel B. The system maps the total size of the lower-sized channel to dual-channel configuration. Any excess memory from the higher-sized channel is then mapped for single-channel operation.

Would someone be able to help me on what this means, and how it affects performance in any way (the only situation I push my rig is for gaming).

You guys are a great help... (I work well with analogies)!
a b } Memory
February 24, 2010 5:28:53 PM

Quote :


You may install varying memory sizes in Channel A and Channel B. The system maps the total size of the lower-sized channel to dual-channel configuration. Any excess memory from the higher-sized channel is then mapped for single-channel operation.

It means that if all four DIMMs are occupied, Dual Channel is enabled, but to the lower RAM size (if not equal). This is another reason why the "matching pair" is always recommended.

For example, let's use the RAM combo you mentioned.

DIMM slot 1: 1GB
DIMM slot 2: 2GB
DIMM slot 3: 1GB
DIMM slot 4: 2GB

With that configuration, you'll end up with 2GB of Dual Channel and 4GB of Single Channel.

*NOTE* The above mentioned example is assuming that you have 2 x 1 GB sticks, as opposed to 1 x 2GB. If in fact you have 1 x 2GB and you want to add two 2 x 2GB sticks, I don't think your board will even boot. On the other hand, if you have 1 x 2GB and want to add one 4GB stick, you can install it, but you'll be limited to the 1GB in the dual channel setting.

For the record, 2 x 1GB in a Dual Channel set up is better than 1 x 2GB in Single Channel even though the physical RAM value is the same.
March 5, 2010 12:49:51 PM

Best answer selected by psylentstorm.
!