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New to OCing, FSB to Ram Ratio?

post #1 of 6
Thread Starter 
Greetings, I've been building systems for a few years now and up till now ive only done minor oc's. Anyway I just recently built this rig and I want to try my hand at a more serious overclock. The problem/question that I have has to do with the relation between fsb and ram speeds.

From what I understand there is a direct relation between the fsb and the ram speed. Now saying that I were able to theoretically oc my proc to 4.0ghz (250 fsb x 16 multiplier) wouldn't this also have the ram running at 250 (at a 1:1 ratio)? So wouldn't this mean that the ram would technically be trying to run at ddr2 1000 speeds? I really doubt that the ram would be able to run at that kind of level.

Now to my understanding I would want to lower the speed of the ram by altering the memory divider to compensate for the oc. For instance, I would want to set a ratio of 4/3 cpu:ram, to have the ram running at the suggested ddr2-800 speeds. This is where my confusion is though; the correct usage of the memory divider. Is this how to use the memory divider and would this be what i need to do?

On a side note, I would just replace my current ram with ram rated for ddr2-1000 speeds but I use a lot of audio production/composing programs that need a high amount of ram and if I went up to ddr2-1000 it seems like I wouldn't be able to put in 4gigs due to a lack of 2 gig sets (which ill be doing with in the next weekor so).

So am I correct in this assumption or am I completely off base?

(Btw ive been using this site for a while now as a general source of info and you guys are great, thanks ahead of time for the help)
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post #2 of 6
Welcome to the forums.

DDR runs as twice the external clock frequency, so you'll be at DDR500 and not DDR1000. The main difference between DDR and DDR2 is the pin configuration; the primary reason the DDR2 speeds are faster is that the newer systems use DDR2, and those systems run at higher frequencies (thus the need for very fast DDR2). Both DDR and DDR2 come in common speeds like 400.

Anyway, it sounds like you have the basic concepts down but that you have an extra factor of 2 in there. CPU FSB = 4x external clock speed; DDR frequency = 2x external clock speed (or 1/2 FSB).
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post #3 of 6
Thread Starter 
Thanks for the speedy reply, and yes for some reason i assumed that ddr2 speeds were 4 x fsb, while ddr being 2 x fsb. I think the assumption came from the my fsb being stock at 200mhz and the ram native speed being 800mhz (800 / 200 = 4).

So if ddr2 = fsb X 2, that means that ill have to use the memory divider in the other direction, aka running the memory 4:5, cpu:ram?
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post #4 of 6
Yup, it's not uncommon to go with crazy fast RAM speeds on higher end systems. Although a 1:1 ratio is often quoted as being optimal, there is the potential for a significant performance boost by really cranking up the RAM frequency even if the CPU can't be pushed that hard. There are a couple of threads around about Corsair 8000UL, one of the fastest products on the market that may interest you (at least one has some benchmarks at various speeds if I remember right).

Anyway, your CPU runs at 200 MHz, so at stock speeds, you could run a 1:2 CPU:RAM ratio. Most likely you'll want to overclock your CPU significantly (Preslers have a great OCing track record), so you'll likely not push things quite that hard. I'd suggest leaving things at 1:1, essentially underclocking your RAM, until your find the max for your CPU (since your RAM will be underclocked, you won't have to worry about tweaking CPU and RAM settings at the same time). At that point, start to crank up the RAM and see how much of a performance increase you can get with a divider that favors the RAM.
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post #5 of 6
Thread Starter 
So does that mean if my rig was kept perfectly stock there would be an auto 1:2 ratio favoring the ram, if the ram was run at its native speed?

Thank you much for the help btw.
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post #6 of 6
That depends on how your mobo detects RAM speed. It may default to 1:1, or it might set it at the actual stock speed. Check in your BIOS and/or use a program such as CPU-Z (available in our download section). That'll give you all the info you need on how things are currently configured.
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2x250 GB Seagate RAID 0 + 320 GB Seagate Samsung SATA DVD Windows XP Pro/Vista Ultimate 64 bit Viewsonic VA2012wb 
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