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Understanding memory

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October 21, 2010 2:43:03 PM

Hi all,

I'm a bit confused...
I have just bought two additional RAM modules for my desktop computer so now all of the four available slots are occupied. Each module is 2GB.
Before buying I checked my old RAM. According to Speccy they are both DDR2 PC2-8900. Then Speccy lists some JEDEC info:
#3: 555,6 MHz, CL6
#2: 400 MHz, CL5
#1: 333,3 MHz, CL4

Alright, so I thought that if I bought some 800 MHz CL5 mermory, everything would be great. The JEDEC info for the new RAM modules is as follows:
#3: 400 MHz, CL5
#2: 266,7 MHz, CL4
#2: 200 MHz, CL3

So, now the two new modules are running at 400 MHz, CL5 - I understand that with DDR2 RAM the effective frequency is the double so I guess that is OK.
The old modules are running at 555,6 MHz, CL6. That would be 1111,2 MHz when doubled.

I do not get it; why do the old modules not run at 400MHz, CL5? Would that not result in better performance?

Thanks in advance.
Mathias Brandt.

More about : understanding memory

a c 163 } Memory
October 21, 2010 2:55:34 PM

Hi Maini and welcome to Tom's forum.

Download and use CPU Tweaker and let me know the timings that u get in that program.
a b } Memory
October 21, 2010 2:56:20 PM

You are probably looking at the specs on the RAM in whatever program you are getting the info ! -- a system will not run different modules at different speeds at the same time (all 4 modules are run at the same settings and timings - which is why you need to make sure they can run together - there is no way to have a MOBO run 2 slots at 1 speed and the other 2 at another speed just doesn't work that way !)

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October 21, 2010 3:09:40 PM

CPU Tweaker would not run, so I used MemSet instead. It gave me this:



According to that, both channels are running with the same timing, and, I guess, the same frequency (800MHz). Correct? :) 
a c 163 } Memory
October 21, 2010 3:19:38 PM

Correct

CPU-Z always list all the possibles frequencies that was all that u listed previously. Lik JDFan any mobo only can run the RAM at one speed and always is the lowest speed that in ur case is 800MHz.
a b } Memory
October 21, 2010 3:22:39 PM

The programs are reading the contents of the little SPD chip on each stick. Your BIOS will actually determine the single speed that the motherboard is going to run the memory.
October 21, 2010 3:37:24 PM

Aha, that actually makes sense ;) 
Now, I am hoping for a performance boost in e.g. Civ5 which recommends 4GB RAM.

Anyway, thanks a lot for your help :) 
a c 163 } Memory
October 21, 2010 3:48:38 PM

Performance games depends mostly of the GPU.
October 21, 2010 4:04:55 PM

Yep, I know. However, Civilization V is really CPU intensive (that is why they recommend a quad core CPU and 4GB RAM). The graphics in the game, although pretty, are not as demanding as an FPS game.
!