Re: DRAM to CPU Frequency Ratio (Athlon)

From: Ookhoi (
Date: Mon Aug 28 2000 - 00:40:19 EST

Hi Marc,

> > 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.
> >
> > 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).
> >
> <snip>
> You have PC133-333 RAM installed (PC133-222 SDRAM is still hard to find)
> which may also be run as PC100-222. So, when you select a ratio of 3:3,
> then the RAM runs in PC100-222 mode, which is not too much slower than
> PC133-333:
> 2*1/100e6 = 1/50e6 is actually smaller than 3*1/133e6 = 1/44e6.
> There are _many_ factors to SDRAM timing, but the bottomline is that you
> will only see a difference (of then ca. 5%, which sounds tiny, but is
> approximately the same gain as when going from a 600 to a 650 MHz CPU)
> if you use PC133-222 SDRAM.

Thank you for your reaction. Others on the list also said that with a
kernel compile, disk speed is a bottleneck, not memory.

What is the difference between PC133-333 and PC133-222, and is that also
the difference between RAM and SDRAM? Do you have an url to more info
about this (and other factors to SDRAM timing)? TIA!

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