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# Convert Memory Speeds

How do you convert a memory speed in megahertz to the PC rating?
Example: PC3200 memory runs at 200MHz (I know it may be 2x that because of DDR) so my memory at 224MHz would run at PC3500 or something. What exactly would it run at?
It depends on the platform you are using. Intel and AMD use different speeds methods.

Intel has quad pumped data busses. Now data is transferred on the rise and fall of the sine curve. Single data rate dram ran on the maxima of a single harmonic quadratic sine curve. Remember your Quadratic equations? The curve? Well, the top of the curve is the maxima of the data transfer. So single data rate dram ran at a theoretical maximum (Spec) of 133MHz.

Then came about a new translation called “DDR” where the data was now being transferred at double the theoretical rate and transferred at the maxima and minima of the sine curve. One stream at the top of the curve and one stream at the bottom of the curve. So you had 133 X 2 which brought about DDR at 266MHz or PC2100. Then the streams were increased to 166MHz X 2 which brought about 333MHz or PC2700. Then again the streams were increased to 200Mhz which brought about 400MHz or PC3200.

Then came about DDR2 where the dram was now running on two async sine curves with two streams at the maxima and two streams at the minima. There had to be an increase in latencies to deal with the offset data streams. Something like having one singer with two tracks of singing just slightly offset from each other to add depth to the song. Well, there had to be a latency increase to allow the two streams of data to move without intercepting each other. Now two streams at the maxima and two streams at the minima bring four streams (theoretically, as seldom do you have all four streams transferring in concurrency) in one tick of the clock which is the rate of DDR2.

This is how the dram works. However this is how Intel makes use of this dram. They quad pump their data at the processor so that it runs in four concurrent (theoretical again) streams and drops from the CPU to the cache in the same way and then to the dram in the same way.

Something like how runners have to both hand off and receive the baton is a way to think of the transfer from CPU to Cache to Memory.

Now AMD does not work the data this way. AMD runs off of PC3200 at 400MHz. Since AMD has their memory controller on chip and the theoretical transfer rate is so high there is no need for them to go Intel's route.

For AMD HTT (Hyper Transport Technology) is used to transfer data from memory. For s754 the HTT is 1600MHz and for s939 its 2000MHz so there is no need for the method Intel uses. It is a more elegant method of data transfer but can be a problem since new methods of data and data transfer mean a chip revision and with Intel it just means a chipset revision.

Your Memory on an AMD platform will run at it's theoretical maximum and the ability of the chipset to source the memory. The data transfer numbers that that AMD gives out are more to look competitive with the Intel numbers.

224MHz X 4 = 896 X 4 = ~PC3584

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great information rep to u...maybe you should make a FAQ about that!!!!!
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Quote:
 Originally Posted by Leprachuan great information rep to u...maybe you should make a FAQ about that!!!!!
I'll tell you what Leprachuan. I'll yapp off as I am really good at that and you can compile my yappings into a faq. How's that sound.

LOL

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Lol, Ropey, you did a great job explaining something, but I think you missed the actual question. To answer your question, there is no way to convert it really. You just have to look at a chart and pick whichever one is closest to yours. Or have everest tell you
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Quote:
 Originally Posted by Fishie36 I think you missed the actual question.
Did I?

Quote:
 Originally Posted by nightdagger How do you convert a memory speed in megahertz to the PC rating?
Quote:
 Originally Posted by Ropey So you had 133 X 2 which brought about DDR at 266MHz or PC2100. Then the streams were increased to 166MHz X 2 which brought about 333MHz or PC2700. Then again the streams were increased to 200Mhz which brought about 400MHz or PC3200.
Quote:
 Originally Posted by Ropey 224MHz X 4 = 896 X 4 = ~PC3584 MHz
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Ropey, that's a great answer. I also think you should make a FAQ about it.
However, allow me to give a simple answer in the hope of answering nightdagger's question.

Facts:
1) Data is transferred 8 bytes at a time (per cycle).
2) DDR memory transfers data at a double rate.

Formula:
So we get the following:
Normal Transfer Rate = (memory bus clock rate) × 8 (number of bytes transferred).
DDR Transfer Rate = (memory bus clock rate) × 2 (for double rate) x 8 (number of bytes transferred)

Application with numbers:
So with a bus frequency of 200 MHz, DDR gives a max transfer rate of 3200 MB/s.

Transfer Rate = 200 MHz × 2 × 8

Thus the notation of PC3200 for DDR400.

A final word:
If you add to that the fact that most modern machines make use of "Dual Channel" technology you would get a total transfer rate (bandwidth) of 3200MB/s x 2 = 6400 MB/s

Hope this helps.
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Quote:
 Originally Posted by Ropey Did I? R
Maybe not... It's just so long and drawn out. It confused me and probably the person that asked it
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Quote:
 Originally Posted by Fishie36 It confused me

I'm sorry that you felt so confused by my ramblings that you missed the answer to his question.

Maybe he will now get the more condensed version from the above post.

Thanks for helping me to condense.

Edit: Good work Zone

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Quote:
 Originally Posted by Ropey I'll tell you what Leprachuan. I'll yapp off as I am really good at that and you can compile my yappings into a faq. How's that sound. LOL R
nah....way to much effort for me.
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