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Author Topic: Read this when your memory speed seems too low  (Read 16588 times)

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HansTopic starter

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Read this when your memory speed seems too low
« on: 28-November-07, 06:16:23 »

You noticed that your memory is not running at the speed that you expected and you are wondering
why that is. Here is the most likely answer to that.

Many monitoring programs don't show you the double data rate (DDR) of your memory. So, first, multiply your memory frequency by 2 to get the double data rate. For example, when using PC4300 ram, you get a memory frequency of 267MHz, in stead of 533MHz. 266 is only half the speed of 533, so your monitoring program shows single data rate, not double. With PC3200 it goes 200/400MHz, etc.

The second thing you should consider is the following. The combination of certain memory frequencies and CPU-speeds make it impossible for the memory/cpu to run at full data rate specified by the memory manufacturer. I'll take my own system as an example to show what I mean.

 - 2 Opterons 2212, running at 2000MHz.
 - PC4300 memory installed. Maximum speed is 267 (single data rate) or 533 (double data rate) MHz.

Now, the following happens: To get the right memory clock speed, the cpu speed is divided by a number. In this case, it would be:

          2000/266=7.5 .

This outcome is not possible for the CPU. It needs a round (solid) number. In this case the choice is between 7 and 8. However, when using 7, chances are that the system will not run stable, because the outcome is higher than the memory can handle (guarenteed):

          2000/7=286MHz (572MHz DDR).

So, the higher numer (8) is chosen, giving this result:

          2000/8=250MHz (500MHz DDR).

In my case, CPU-Z reports a data rate of about 250MHz. Note the first remark I made: you need to
multiply by 2, to get the doube data rate (DDR) speed: 500MHz.

If you oc the cpu speed slightly, memory speed will increase a bit as well. Example: when overclocking the cpu to about 2125MHz, the memory will start running at the speed it can handle:

          2125/8=266MHz (533MHz DDR).

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cybermac912

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Some clarification, please
« Reply #1 on: 15-December-07, 23:48:19 »

Does the number of memory chips affect this behavior? I have two 1GB PC3200 chips for my MSI KT8 Neo FISR. When I run each one separately, it registers as 200MHz (DDR400) in memtest86. When run together, they register as 100MHz (DDR200). This alarms me to no end, but it sounds like this is expected, yes? If so, why do they "appear" to run at full speed singly, but half-speed running together? And will the actual speed of the two running together match the speed of one by itself (otherwise, I'll see a performance hit when upgrading from 1GB to 2BG)?

Sorry for the newbie-sounding question, but memory's been over my head since my 72-pin's went out of style ;-))

Thank you
= Eric
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Aaron

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Re: Read this when your memory speed seems too low
« Reply #2 on: 15-December-07, 23:52:41 »

Just manually set the speed in the BIOS.

It shouldn't effect it using the two sticks, but it's most likely for compatability.
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cybermac912

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Re: Read this when your memory speed seems too low
« Reply #3 on: 16-December-07, 00:09:07 »

Hmm, I was hoping you wouldn't say that :( I've tried numerous combos of manual frequency and timing settings. Nothing seems to force the memory to run faster, at least according to memtest. The only thing that had a marginal effect was overclocking the FSB. When I set the bus to 250 MHz, the two sticks ran at 125 MHz. The upside is that my processor ran faster, but still I feel like I'm being cheated of performance.
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Re: Read this when your memory speed seems too low
« Reply #4 on: 16-December-07, 00:15:34 »

Use CPU-Z in Windows to verify speed.
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Refrain from having to solve most of your problems by not creating them in the first place.

DDR3 Memory Standards: Blurry Lines
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Svet

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Re: Read this when your memory speed seems too low
« Reply #5 on: 16-December-07, 00:43:50 »

@cybermac912

Read Moan Guide and provide full details about your PC, then open your new own topic.
Do not post/reply here.
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Cirap

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Re: Read this when your memory speed seems too low
« Reply #6 on: 23-December-07, 10:25:44 »

just noticed with my system:

If you run a 2800Mhz ( 5600+) processor with DDR2 667MHz the memory will only run in 311Mhz (622MHz DDR), because the CPU:DRAM multiplier is 9, rather than 8  (which would run the RAM in 700Mhz which is too high), or 8.5 (~660MHz) which isn't possible

thus, if you want your 667MHz memory to run at full speed you'd need a 3.0Ghz processor (6000+)

this simply means you can OC that 5600+ to 3.0GHz without getting any problem from your RAM. that's a good thing  :biggthumbsup:

and I also have Crusial XMS which are guaranteed to run at 675Mhz, so I can go even further without getting blocked by my RAM
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HansTopic starter

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Re: Read this when your memory speed seems too low
« Reply #7 on: 26-December-07, 04:06:00 »

Like BK already said: this topic is meant to provide some info on memory speed and the possible cause of your RAM not running at full speed.

This is not meant to post in. I'm locking this topic to prevent further discussions/posts in here.
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You have a Q-Tec Power Supply? Change that first and come back later...

* MSI P55-GD85, bios 1.3
* Intel Core i7 860 (stock @ 2.8GHz)
* 2x 2048MB TakeMS @ 1333MHz (8-8-8-24, 1T)
* Club3D HD5770 1024MB
* OCZ Vertex 2 120GB (OS and apps)
* 5x Western Digital Caviar Green 500GB in RaID5 (storage)
* 2x DVD Rewriter (LG, Optiarc)
* PC Power & Cooling Silencer 750W
* Cooler Master Stacker CM101
* Dell Ultrasharp 2209AW 22\\\" (e-IPS) monitor
* Windows 7 Professional NL

MSI MediaLive: AMD Athlon X2 4800+, 2x1GB Crucial PC-4200, Seagate 160GB, Pioneer DVD-burner, Hauppauge PWR150 TV Tunercard, Windows 7 Home Premium NL.

MSI X-Slim X620 :like: :like:

Backup: Thecus N5200Pro NAS
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