Re: DRAM to CPU Frequency Ratio (Athlon)

From: Stephen Frost (
Date: Fri Aug 04 2000 - 09:22:57 EST

On Fri, 4 Aug 2000, Ookhoi wrote:

> Hi!
> I have two exactly the same Athlon systems at 750MHz and 512 meg memory
> (@ 133MHz). In the BIOS there is a option: "DRAM to CPU Frequency
> Ratio", which can be 3:3 or 4:3. The Help says: "Using this item to set
> the operating frequency of DRAM".
> I just installed Debian on the machines, rebooted, changed one machine
> to 3:3, the other was 4:3, and compiled a kernel on both of them. The
> time it took was almost exactly the same (about 5 min 32 sec). The 3:3
> one was 0.24 seconds faster.

        It is likely there are other limiting factors.

> Does Linux ignore the DRAM to CPU Frequency Ratio (if at all possible),
> is it just a useless BIOS option (because of hardware limits or
> something), or is it not supposed to make the machine faster (if, what
> _does_ it do then ;-) ? (the book that came with the machine doesn't
> tell me much about the option).

        The question is what is the ratio between the speed of the CPU
bus and the speed the DRAM should run at. 3:3 means same speed, 4:3 means
the DRAM runs faster than the CPU. If you CPU runs at 100mhz for it's
communication to the chipset and you use '3:3' then your memory also runs
at 100mhz. If you use '4:3' then your memory runs at 133mhz while the
CPU runs at 100mhz. etc, etc.


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