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Need a couple pointers overclocking my CPU

Need a couple pointers overclocking my CPU

Postby Cornflake » Fri Oct 24, 2008 3:26 pm

Hi all,

I decided to take up overclocking my AMD 5000+, because I have a good cooler on there (Zalman 9700CNPS or what not) and don't have the money to buy a new CPU at the moment. However, I have a couple questions. First I did some googling and found this post on the AMD forums that has helped answer most of my issues. I have the PC overclocked to about 2.8GHz, running stable but I'm running into an issue with my RAM...

Apparently the RAM speed raises with your CPU frequency (Called FSB?) and so that means I have to run my DDRII at 667MHz instead of 800MHz when overclocking, or it will set me over my RAM's rated max of 800. Ie if I overclock to 3.0GHz and we do the math: Ram DDR speed = (CPU FREQ/RAM DIVISOR) x 4 then that works out to be 3000/13 = 230.76x4 = 923 and I dont think running my RAM 123MHz over the limit is a good idea. But if I run my RAM at 667MHz then 667 + 123 = 790 so it will run close to my original speed.

Here's where my true question lies: Before I got into this I was expecting I'd be able to change my CPU Multiplier and things would of been so much easier. Ie I could raise it to 15 and everything would work out -- 200 (CPU FREQ) x 15 = 3GHz, and even my RAM would stay at a perfect 800: 3000/15 = 200*4 = 800. But, my BIOS will not let me raise the multiplier above 13. Why? And also, the RAM Divider is the same thing as the CPU Multiplier right? And what is with the Ram divider ratio - can someone explain that a little better please?

- Thanks a ton!
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Postby ar1stotle » Mon Oct 27, 2008 5:20 pm

Alright, your CPU multiplier is probably locked by the CPU. That's why they make the Black Editions: the multiplier is unlocked so it's a lot easier to overclock. Raising the FSB will increase both the CPU and RAM frequency. The RAM divider, depending on your bios, will either show you a ratio like 1:1 or 1:2, or simply show speeds like 667mhz or 800mhz. If you set it to 667 but raise the FSB, it can still end up running at over 800mhz depending on how much you raised the FSB. I don't know the exact relationship off the top of my head because it's a little different with Intel and AMD CPUs (I think?) and I've been so busy with school that I really haven't had time to do anything new with any of my stuff for quite some time.

So no, the divider is not the same thing as the CPU multiplier. The divider will allow you to up your FSB without making your RAM run too fast. Depending on how good the RAM is, you might be able to get it running around 800mhz or a little higher after the overclock, but you might have to sacrifice some as well depending on if you're trying to max out the CPU or try to find a stable combination (which, if you sacrifice some ram speed, you could possibly tighten up the timings a little to compensate).

Hope that made sense.... gotta get back to studying now lol

BTW if you boot to a memtest disk after you overclock, it should tell you exactly what frequency the ram is running at. I'd probably do a little more searching so you can at least get a good guess of where to start with the divider so you don't end up getting an unbootable system and not knowing how far over you went.
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