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Running 800 MHz FSB at 533 MHz

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September 16, 2004 2:37:01 PM

Hello gurus --

I must admit I am new to the P4 market (too poor to afford them until now). I am trying to slowly convert my old AMD system over to a new P4 system. I want to do this in incremental steps, but I am running into some problems determining if it is possible or not. I did try searching the forums and the net before I came here, but I was unable to find anything useful (maybe I was searching the wrong key words /shrug).

First, I picked up a Soyo "SY-P4I865PE Plus Dragon2 V1.0" mobo and I am now working on getting the proper CPU. I am considering buying the P4 3.2(E) GHz Prescott with a 800 MHz FSB. However, I currently have 4x256MB of DDR266 (PC2100) memory that I would like to use initially. I know that PC2100 memory cannot run with a 800 MHz FSB, but I want it to be the first step in my conversion.

My question is can underclock *gulp* an 800 MHz FSB down to 533 MHz to run with my PC2100 for the time being, and are there any side effects... I'm assuming a lower CPU speed, but is there anything else that I am missing?

In another couple months I plan on upgrading to 512/1 GB of DDR400 to greatly improve system performance, but I really want to know if I can set to 800 MHz FSB to 533 MHz until I get a little more cash. Of course if anyone wants to send me a little extra cash, we can skip this process. :) 

Thanks for the help!
-- J --
September 16, 2004 2:41:07 PM

That would be a catastrophic success.

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September 16, 2004 2:46:17 PM

Why can't you run your CPU at 800 Mhz FSB paired wtih 2100 RAM? Granted, it's good to try to match them, but it's not a requirement (and you'll see a much larger performance hit by underclocking your P4).

Am I missing something here? I had no problem doing this with my ASUS P4P800 - until recently I was running a 3.4 Prescott with 1 512 MB, PC2100 stick from Kingston...

I'm just your average habitual smiler =D
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September 16, 2004 4:03:46 PM

See my comments inserted... thanks for the help!

Why can't you run your CPU at 800 Mhz FSB paired wtih 2100 RAM?

>>> Really? You can run PC2100 with 800 MHz FSB, I didn't realize that? It doesn't show up in the mobo manual as an option. Maybe it's not supported by the mobo? It says for 800 MHz FSB, only 400 MHz or 320 MHz memory is allowed(333 MHz underclocked). And for 533 FSB, either PC2100 or PC2700. Async not supported? /shurg -- I don't know enough here to take a guess.



Granted, it's good to try to match them, but it's not a requirement (and you'll see a much larger performance hit by underclocking your P4).
Am I missing something here? I had no problem doing this with my ASUS P4P800 - until recently I was running a 3.4 Prescott with 1 512 MB, PC2100 stick from Kingston...


>>> Maybe I'm missing something... It didn't show up in the mobo manual, so I figured it couldn't be done. Anyone out there using this mobo running PC2100 at 800 MHz FSB?


Thanks again for the help,
-- J --
September 16, 2004 4:26:50 PM

wow, don't listen to that guy he obviously doesn't know what he's talking about.
There's no way you can run ddr266 at 800fsb. you would need ddr400 to do this, 200 quadpumped to 800.
You can underclock it to 533fsb but you will see a proformance hit.

Watch out for the <b><font color=red>bloody</font color=red></b> Fanboys!

AMD64 2800+ :: MSI Neo-Fis2r :: 512mb Kingmax ddr400 :: Sapphire 9800pro 128mb :: 10K WD Raptor

Addicted, finally.<P ID="edit"><FONT SIZE=-1><EM>Edited by DonnieDarko on 09/16/04 12:28 PM.</EM></FONT></P>
September 16, 2004 5:15:30 PM

Well, my computer must have been very confused to have been running this combination correctly. *shrugs*

Currently I'm running my P4 with 2700 RAM (the board sets the frequency to 320 Mhz, instead of the 333 to balance timing issues).

I'm just your average habitual smiler =D
September 16, 2004 5:31:17 PM

it runs but not at 800fsb. Your fsb = ram speed x 4. So if you have ddr266 it's 133 x 4 = 533.

Watch out for the <b><font color=red>bloody</font color=red></b> Fanboys!

AMD64 2800+ :: MSI Neo-Fis2r :: 512mb Kingmax ddr400 :: Sapphire 9800pro 128mb :: 10K WD Raptor

Addicted, finally.
September 16, 2004 6:01:14 PM

Quote:

wow, don't listen to that guy he obviously doesn't know what he's talking about.
There's no way you can run ddr266 at 800fsb. you would need ddr400 to do this, 200 quadpumped to 800.
You can underclock it to 533fsb but you will see a proformance hit.



you can run your ram a-synchonous of your fsb

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September 16, 2004 6:14:34 PM

You're forgetting about FSB:MEM dividers!! A 3:2 divider will run them async (800FSB:533DDR [effective]), and you'll lose only bandwidth, not clocks and bandwidth. However, I don't know if your board has a 3:2...so using the lowest divider and then underclocking might be necessary.

Maxtor disgraces the six letters that make Matrox.
September 16, 2004 6:27:23 PM

I know that, that's why i didn't say his clock speeds wouldn't be different, but he'll still be only running at 533 effective fsb.

Watch out for the <b><font color=red>bloody</font color=red></b> Fanboys!

AMD64 2800+ :: MSI Neo-Fis2r :: 512mb Kingmax ddr400 :: Sapphire 9800pro 128mb :: 10K WD Raptor

Addicted, finally.
September 16, 2004 9:27:35 PM

No, he'll be running 800FSB no matter what the divider is. He'll only get 533MHz of bandwidth (about 4.2GB/s rather than 6.4GB/s), however (there IS a difference!). A P4B 2.8 is slower than a P4C 2.8 running a 3:2 divider (same board, same RAM).

Maxtor disgraces the six letters that make Matrox.<P ID="edit"><FONT SIZE=-1><EM>Edited by Vapor on 09/16/04 05:28 PM.</EM></FONT></P>
September 17, 2004 12:15:23 AM

I believe your board supports a 6:5 mem divider. at 320mhzDDR rate(effective fsb, true fsb is 160). You could set the divider to that, then set your fsb to 160 (640 effective) and still be at factory standards (no overclock) It is quite likely that if you have good ram, drop the timings, and give them a little more voltage, in other words over clock the memory, that you could run above 190 true fsb. If I were in your shoes, that's what I would do.
BTW, you picked the wrong time to switch. Lately Amd has been having more successes than Intel. You have effectively cut yourself off from the fisrt few years of 64 bit.
Dont by prescott, they are a few $ cheeper than the P4c because they are not as good.
September 17, 2004 9:40:56 AM

RAM speed isnt related to FSB, just like on my athlon board when I have the FSB at 333Mhz I can run the RAM at either 266 or 333Mhz.
September 18, 2004 2:18:19 PM

endyen --

Thanks for the info; this is what I was hoping to do. I know that switching over now may not be the best time, but I got the mobo for free (gotta love newegg special deals) and a new P4 3GHz blows away my 1GHz Athlon right now. So for about $150 bucks I am able to increase my overall performance by more than 3 times using a P4. That will hold me over for at least another year, so I think it's worth it -- but it's always a matter of opinion.

Who knows, maybe I won't get the new ram and just stick with the DDR266 and try some overclocking, then just wait for the DDR2 and 64-bit processors to come down in price and stabilize a little bit... besides, last time I checked (okay, it was about a year ago), there weren't really any applications for the 64-bit yet and no OS -- sorry, the wife doesn't understand linux, so that option is out. I'll probably go 64-bit in about another year.

Thanks for the advice on the prescott, I didn't realize they weren't as good as the P4c. I will keep it in mind and do a little more research.

Besides, everyone in my family loves when I upgrade my computer, it means someone gets a new PC that is a huge improvement for free... they never buy PCs! :) 


Thanks for the help everyone,
-- J --
September 25, 2004 3:22:28 AM

What's the P4c? I'm so out of touch with the new CPUs. I've been looking at the 2.4 Prescott since my board (MSI-NEO PT8) limits the Prescott FSB to 533MHz. I'm trying to decide which is better, FSB or Cache. I can use the Northwood 800MHz if I want to.
!