Messages in this thread | | | Date | Mon, 28 Aug 2000 07:40:19 +0200 | From | Ookhoi <> | Subject | Re: DRAM to CPU Frequency Ratio (Athlon) |
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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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