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fsb...multipliers...i don't understand. help plz.

Last response: in CPUs
February 9, 2003 5:15:31 AM

I'm a little confused on how to get a proper cpu / memory combonation. For example, I am wanting to get a AMD XP 2400+. Now that is a 266 fsb processor right? Does that mean that I shouldn't get a 333 or 400 fsb ram? pc2700 = 166mhz fsb so why do people refer to it as 333?

So it doesn't make since to buy 333mhz ram (like pc2700) without matching it up with a 333mhz processor (like amd xp2600 or higher), right?

Ultimately, I don't want to overclock anything. I'm just trying to figure out what ddr memory to use with the xp2400+ (by the way what does the '+' mean on that? Does that mean it's better?). I heard that if the cpu and memory fsb speeds don't match up then you have to run them with a-syncronous timings or something...which means unstability...

Sorry for the newb questions. Any help would be appreciated, or if you could point me to a website that lays down all this information and would help me learn I'd appreciate it. Thanks!

February 9, 2003 5:35:13 AM

1. You can always match your 266fsb cpu with 333fsb ddr ram but if running in sync is somehow better performance.
2. The 333fsb means that 166mhz x2=333mhz fsb.
3. The 2400+ is called P-rating. It means that when comparing this cpu to p4 2.4 it's actually more powerful.
4. If running in sync the system performance will increase but even not sync doesn't mean your system is in instability.
hope this helps, cheers!!!

My PC has gone to hell... because it's a killing machine...
February 9, 2003 8:19:58 AM

Hmmm okay...well take a look at this page here:

Tom is reviewing some Shuttle xpc, and in the first paragraph it says:

"the SN41G2 AMD platform also offers dual-channel DDR400. Having said that, we don't recommend using this setting since it means running your FSB and RAM clocks asynchronously, and that puts a damper on performance. We've discovered that the best configuration is DDR333 RAM with FSB and RAM clocked at 166 MHz, provided that you have an AMD CPU that offers an FSB clock of 166 MHz (Athlon CP 2700+ or higher). Otherwise, you have to clock your FSB at 133 MHz and then have your RAM running at 200 MHz (DDR400)."

I am still confused by that paragraph. When he is refering to the FSB and RAM being clocked at 166Mhz is he referring to DDR333 (PC2700) and a processor that is running 333MHz fsb like the xp2700 or higher?

If I am going to buy a xp2400+ (running at 266Mhz, right?) would it be best to use PC2100 (DDR266) ram? Then the FSB and RAM are running at the same clock speed, like the above paragraph recommends...

But then in that paragraph above, he makes it sound like it would be even better if I was using a 266Mhz processor like the xp2400+, and also was using DDR400 ram (PC3200 right?) that confuses me even more...He discourages using a processor running 333MHz with ram running 400MHz, but then encourages using a processor running 266MHz with ram running 400MHz...i'm confused...

Any more help would be appreciated.

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February 10, 2003 3:22:51 AM

No one here is willing to help me out? I have had a hard time finding any good websites that discuss the basics for newb's. All the websites I find about these topics are talking about overclocking and all sorts of advanced stuff without offering to explain the basics first. If there is anyone who could point me in the right direction I would appreciate it.
February 11, 2003 2:48:05 PM

I understand your frustration. Sometimes online communities are reluctant to provide basics but there are some people who are willing to help - after all you have to start somewhere don't you? Anyway here goes:

Some of your confusion has arisen from the DDR problem that confused me when it came out. Basically the new 2700+ runs with a 166 fsb but since this has a Double Data Rate (DDR) you multiply this by 2 to get 333MHz. So the ideal setup would be an XP 2700+ (or any with 166FSB) coupled with some PC2700 memory which runs at 166 DDR (333MHz) As a general rule, no matter what CPU you have, faster memory will always be better in your machine. So you could use a 1GHz Duron with PC2700 memory if you really wanted to.

In terms of your machine build, I would go for PC2700 memory and a CPU with 166 fsb. Reason: in the current socket type there will never be a CPU with 200 fsb to match with PC3200 memory (400MHz) and that memory is more expensive for minimal performance gain.

For the best performance I recommend Corsair XMS2700 and for the best results MAKE SURE that you get CAS 2 and NOT 2.5.

Also I would suggest getting an Nforce2 chipset motherboard and buying 2 DDR modules for the best performance possible.
And for the best value for money I suggest waiting for the XP 3000+ to come out by which time the "older" XP 2700+ & 2800+ will be a lot cheaper.

Hope that helps. :) 

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