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Old 08-06-2005, 10:34 PM   #1 (permalink)
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Default RAM speed and CPU FSB speed

I found this in an article about PC building:

"In an AMD based system RAM speed optimally should match that of the Front Side Bus speed of the CPU. For example a processor with a 333 FSB should have ram that runs at 333 MHz. This RAM is commonly known by other names such as DDR 333 or PC2700. There is DDR 266 RAM and DDR 400 as well."

If this is so, what speed of ram would be ideal for an AMD CPU with a FSB speed of 1GHz such as the 3700+ San Diego?

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Old 08-06-2005, 11:02 PM   #2 (permalink)
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AMD64s are a bit confusing as far as the FSB goes.

They technically do not have a FSB, but an LDT or HTT (hypertransport) bus because the memory controller is built directly into the chip. On previous chips the FSB acted as a communication link between the controller and chip but since that is no longer neccesary the high speed, low latency bus directly between the chip and RAM was created.

The HTT is pretty much Memory Speed * LDT Multiplier * 2

Which on AMD64s on socket 939 would translate into:

200 * 5 * 2 = 2000MHz

And since as you may know DDR is double date rate memory the multiplication by two at the end is technically doubling the RAM speed so technically speaking the "FSB" speed or HTT speed is 1GHz.

But to answer your question, AMD64s use DDR400 PC3200 memory
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