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How do you use the 800MHZ FSB?

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June 20, 2003 5:16:38 PM

I just ordered a p4 2.6ghz 800 mobo processor combo. It comes with 3200 512 MB DDR Ramm that runs at 400Mz. How can I utilize the 800Mhz FSB if my ram only runs at 400mhz? Would it had been smarter to just order the regualar 533mhz 2.6?

More about : 800mhz fsb

June 20, 2003 6:25:18 PM

This is indeed a confusing matter.

The current Intel CPU's currently have an *actual* FSB speed of 200Mhz. However, they use a "quad pumped" memory bus that allows the chip to talk to the memory 4 times per clock cycle. Therefore, any advertised Intel FSB speed is only really a marketing term that is 4X the actual FSB Speed. (800 = 200 * 4), (533 = 133 * 4) etc.

Now, your DDR speed is always advertised as double the *actual* speed, because DDR = Double Data Rate, which means it works two times each clock cycle. So, DDR400 works at 200Mhz doubled, and DDR333 works at 166Mhz doubled.

This being said, that means an Intel chip with a FSB of 800Mhz matches up exactly with DDR400. Confusing enough?

And FYI, an AMD CPU with an actual FSB speed of 200MHz is advertised as 400Mhz. So, AMD 400Mhz is basically the same as Intel's 800Mhz FSB

<font color=red>Proudly supporting the AMD/Nvidia minority</font color=red>
June 20, 2003 6:38:52 PM

Hiya madness;

hehe your fine with the ram you have.

The CPU uses QDR and the external frequency clocks at 200x4 = 800Mhz, The DDR clocks at 400x2 = 800Mhz in dual channel mode, thats just how it works, dont change a thing.
There is a certain way to install the ram onto the mobo, you have to use specific slots to achieve Dual Channel mode, also it requires you to use the memory in pairs, you will need 2x256MB, or 2x512MB modules.

I hope this helps.

XeeN
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June 20, 2003 9:38:39 PM

So In order to get the full 800mhz FSB I should have ordered 2 X 256MB of the DDR Ram? Will this show a big difference in performance or is it very minimal?
June 20, 2003 10:26:25 PM

Using a matched pairs of memory sticks is a whole different issue that FSB speed. Great Xeen, you got him all confused.

Your motherboard has 2 seperate memory controllers. Using 2 identical sticks of ram....one for each memory channel...allows each controller to access both sticks, theoretically doubling your memory bandwidth. It would be a significant performance loss if you were not running in dual channel mode.

<font color=red>Proudly supporting the AMD/Nvidia minority</font color=red>
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June 21, 2003 5:30:55 AM

What board/chipset did you get? The 865 and 875 series Intel chipsets are made for dual channel mode. This makes up the difference between your "800" CPU bus and your "400" memory bus by making the memory bus twice as wide. You need a matched pair of modules to enable dual channel mode.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
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June 21, 2003 5:31:59 AM

There are no pumps, it's a "Quad Data Rate" bus. I've looked everywhere, no pumps involved.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
June 21, 2003 3:55:15 PM

I got this one right here:
Asus P4S800 Pentium®4 DDR with 2.6Ghz 478Pin 800FSB CPU And this ram:
1 512MB Certified 400Mhz PC3200 DDR

So what exactly do I need to get the optimumn performance out of this set-up?


<P ID="edit"><FONT SIZE=-1><EM>Edited by madness2003 on 06/21/03 12:34 PM.</EM></FONT></P>
June 21, 2003 6:53:45 PM

Ryan:

I never said "matched", i said in "pairs" meaning 2x256 or 2x512, its plain english you must have misread hehe

Xeen
June 21, 2003 7:25:34 PM

You'll need to get another one of those sticks if you want to run your mem in dual channel mode.

<font color=blue>I feel the need...The need for weed! :tongue: </font color=blue><font color=red><b><i>Jay Kay</font color=red></b></i>
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June 21, 2003 10:49:51 PM

As long as the module is top quality, buy another, and you'll have 1GB operating in dual channel mode.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
June 24, 2003 2:05:42 PM

Ok i got the 2 X 256MB of DDR 3200ram. Now if I wanted to add ram in the future can I just add a 512 stick or do i need to continue to add ram in pairs?
June 24, 2003 2:48:58 PM

Pairs, which means you'll be full now. If you ever wanted to upgrade past a Gig you'd need to sell or get rid of 2 of the 256 meg sticks and buy 2x512.

--Xenius
-non computer guru
June 24, 2003 2:59:04 PM

madness2003, maybe you should just return everything and buy a Dell or something. Just a thought...

"<i>Yeah, if you treat them like equals, it'll only encourage them to think they <b>ARE</b> your equals.</i>" - Thief from <A HREF="http://www.nuklearpower.com/daily.php?date=030603" target="_new">8-Bit Theater</A>
June 24, 2003 4:01:23 PM

Has anyone actually seen a difference in running from un-matched or matched pairs of memory, for either AMD or Intel?

My system: Intel Pentium 4 2.8, 800 FSB / TwinMOS 1Gb DDR400 / ASUS P4P800 / Sapphire Radeon 9800 Pro / Antec True Power 550W / Western Digital Raptor / Hercules G.T XP /
Samsung DVD / Lite-On CDRW
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June 25, 2003 1:37:50 AM

In order to maintain dual channel mode you always have to have pairs.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
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