Memory speed vs AMD memory controller

J

Jeroen1000

Limp Gawd
Joined
Sep 17, 2010
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266
Hey everyone,

I've tried to google an answer but it led me nowhere. I've read here and there that the AMD memory controller runs at the same speed as a CPU core. So, that does not make sense to me at all. Some AMD's run at 2.8 GHZ, some at 3.4 GHZ, etc...

My question is: what is the correlation between the frequency of the memory controller and the frequency of the DRAM. Why is DDR3 @ 1333 sufficient for my Phenom II X3 720? Where can I see what frequency the controller is running at?

Thanks for pointing me in the right direction.
 
The memory controller supposedly will only run at a max of 1333 (I believe, at least that's how I understand it from my reading on it) but ram can run faster. I am not entirely sure if that's true or if it will run at 1600 with the ram or what exactly.
 
Yeah I can't really make sense of why you need to overclock the CPU in order to go higher than 1333 MHZ RAM. I'm surpised the internet isn't full of articles explaining this really.
 
DDR3 @ 1333 is the maximum supported ram frequency for any current AMD CPU. It does not matter what frequency the memory controller is running at but what frequency of ram that memory controller supports. Sure you can use higher speed ram than the IMC was designed to use but that is considered overclocking the ram controller.
 
Googling on "AMD northbridge" in conjunction with "overclocking" were the magic words. Previously, I had been googling on "IMC" and "Integrated memory controller".

drescherjm is right, I'm just looking for how you can see you are overclocking the IMC (I'm getting there, it was just very late yesterday and I stopped reading further).

I 'm stuck in the past when the FSB and memory frequency were 1:1 you know:D
 
I 'm stuck in the past when the FSB and memory frequency were 1:1 you know
Click to expand...

I suspected that had something to do with your questions. Remember in that case the memory controller was on the motherboard and it did not have a separate connection to the CPU like the memory does now. The link between the north bridge and the CPU was the FSB.
 
Interesting. So in the end, why do you need to overclock the CPU as well?

I was assuming the PLL was locked in a way so the clock distribution was in a specific ratio, but like the hypertransport and the memory controller can be dynamically clocked down.

Hmm. Perhaps the user is only allowed to control the PLL for clock division (for power management), but we can only control a single clock multiplier within the PLL before it gets sent to different dividers for each component of the system?
 
The PLL stuff is over my head but basically, if you increase the memory bandwidth (by overclocking the RAM memory + the integrated memory controller) you need to make sure the CPU is also able to use this extra bandwidth.
So, if you do not overclock the CPU, it will not be able to use said additional bandwidth.

The Hypertransport link, is a link between the CPU and the rest of the system EXCLUDING the link between the CPU and the IMC. So this link is really not all too important in an overclock. There are reports though that overclocking the hypertransport link aids in overall system stability.

Both the ICM, CPU and hypertransport link derive their frequency from the Base Clock. The Base Clock on all(?) AMD cpu's is now 200 MHZ. Multiplying the base clock with a certain number yields different frequencies for: the CPU, ICM and hypertransport link.

I hope the above is correct?
Oh yes, also, the ICM does not run at the same speed as the CPU any longer (because of what I rambled on about above). AMD changed this I just can't remember when (I've read a whole lot today lolz). Also, it would be a lot less confusing if overclockers did not use the term FSB anymore. It no longer exists.
 
Last edited:
Jeroen1000 said:
The PLL stuff is over my head but basically, if you increase the memory bandwidth (by overclocking the RAM memory + the integrated memory controller) you need to make sure the CPU is also able to use this extra bandwidth.
So, if you do not overclock the CPU, it will not be able to use said additional bandwidth.

The Hypertransport link, is a link between the CPU and the rest of the system EXCLUDING the link between the CPU and the IMC. So this link is really not all too important in an overclock. There are reports though that overclocking the hypertransport link aids in overall system stability.

Both the ICM, CPU and hypertransport link derive their frequency from the Base Clock. The Base Clock on all(?) AMD cpu's is now 200 MHZ. Multiplying the base clock with a certain number yields different frequencies for: the CPU, ICM and hypertransport link.

I hope the above is correct?
Oh yes, also, the ICM does not run at the same speed as the CPU any longer (because of what I rambled on about above). AMD changed this I just can't remember when (I've read a whole lot today lolz). Also, it would be a lot less confusing if overclockers did not use the term FSB anymore. It no longer exists.
Click to expand...
AMD changed the clock of the IMC when the first Phenom core (Agena) was released. The IMC now runs at the same speed as the CPU NB clock, anywhere from 1.0 - 2.6GHz.

The reason you need to overclock to use higher speed memory is because the RAM clock is derived from the reference HT clock of 200MHz, currently on AM3 processors, the multipliers supported are: RefHT divided by x times y = memory clock (x 2=data rate)
(200MHz HT)
1:1 = 200/400; 3:4 = 266/533; 3:5 = 333/667
1:2 = 400/800; 3:8 = 533/1066; 3:10 = 666/1333
1:4 = 800/1600; for AM3+: 3:14 = 933/1866 and maybe 1:5 = 1000/2000
If you overclock to 250MHz HT, you get higher ram clocks:
1:1 = 250/500; 3:4 = 333/667; 3:5 = 416/832
1:2 = 500/1000; 3:8 = 667/1333; 3:10=833/1667
1:4 = 1000/2000; for AM3+: 3:14 = 1166/2133 and 1:5 = 1250/2500
 
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