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Lower Performance on i875P After Increasing Memory


TSimonick

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I have an Intel 875PBZ (v. AAC26680-205) with Pentium 4, 3.0 GHz and 2 sticks of Corsair 512MB 3200C2 XMS. I have been running this config for 2 years. The BIOS SDRAM Timing is set to Auto and the Frequency was 400 MHz. The latencies for this pair are 2.5-3-3-8 in dual channel mode. Intel PAT was on according to SiSandra. BIOS v. BZ87510A.86A.0076.P33.

I just added 2 more sticks of CMX512-3200C2 XMS. Using the Auto config, the memory speed as dropped to 320 MHz and the timings for the new pair are 3.0-3-3-8. SiSandra is reporting that PAT is now off. My memory bandwith has dropped from 6400 MB to 5312 MB.

 

Why has my memory performance decreased by adding the additional Corsair memory?

Thanks for your thoughts!

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If you run more than 2 sticks in your motherboard, you will lose both PAT and will drop your dram speed one level.

 

If you install DDR400 in 2 slots you will get PAT and DDR400. If you install DDR400 in 4 slots you will have a disabled PAT and DDR333 as the Northbridge memory controller drops these settings to maintain the ability to work correctly.

 

This carries on with the newest boards and systems as well.

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If you run more than 2 sticks in your motherboard, you will lose both PAT and will drop your dram speed one level.

 

If you install DDR400 in 2 slots you will get PAT and DDR400. If you install DDR400 in 4 slots you will have a disabled PAT and DDR333 as the Northbridge memory controller drops these settings to maintain the ability to work correctly.

 

This carries on with the newest boards and systems as well.

 

QFT. However, the newest boards and systems no longer use DDR1 (DDR400) memory -- but DDR2-800 memory instead. However, the fact about the memory controller slowing down when fully loaded remains: DDR2-800 memory controllers will drop the maximum memory clockspeed down to DDR2-667 or even DDR2-533 with more than two sticks of memory installed.

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