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800mhz FSB requires 3200?

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aharpro26

Registered
Joined
May 20, 2004
Location
Canton, OH
I have heard that all Pentium 4 CPUs that run at 800mhz FSB requires 3200 DDR RAM. Is this true or will it run with 2700?
 
With PC 2700 the processor will be downclocked, unless you overclock the 2700. The majority of PC2700 can't hit 3200 speeds without going to extreme measures. So to the point, get some PC3200 if you are going to run an 800 MHz FSB processor.
 
So there is no way to get my CPU running at 800mhz FSB with PC2700 DDR RAM. Or there is? What are dividers?
 
Well, take the 6:5- Divider in BIOS and your RAM will run at 166MHz.
But anyway, you should grab new ram, I recommend PC4000. They run at 250MHz, which allows you to raise FSB and CPU clock
 
The 800MHz bus is actually 200MHz x4.

Hence, with an 800MHz CPU the RAM usually runs at 200MHz (DDR) which is PC32000. This would be at the default 1:1 ratio.

However, your board may have other FSB:RAM ratios that you can use. If your CPU has a 200MHz FSB and you have RAM that can only do 166MHz (333MHz DDR, PC2700) then you need to select a suitable ratio for this.

200:166 = 6:5 ratio.

So if you select a 6:5 ratio this will allow you to use 166MHz RAM :)

Let me know if you want anything explained a bit clearer - it can get quite complicated :)
 
Or you're just not going to get the bandwidth but it will run. I had to rma my kingston 3500 chips and I used some pc2100 sticks at dual channel to see if it would work. I was expecting my cpu to say 1500mhz but I was able to boot at normal cpu speed but lost 2 gigs of bandwidth. This may have been an anomaly. I wouldn't bottleneck the bandwidth for long though.
 
You need to tell us what motherboard you have, but generally you can use the proper memory ratio and your PC2700 will work. I've seen two people say 6:5 ratio, but I don't know of any common P-4 overclockable mobo having that ratio. With the i865/i875 chipset mobos with a 800 bus CPU, you'll have three choices: 1:1, 5:4, and 3:2 ratios.

If you use the 5:4 ratio, you can overclock up to 208 FSB and still have PC2700 RAM in spec. Obviously, if your RAM overclocks well, you can go higher. If you use the 3:2 ratio, then you can overclock up to 253 FSB and still be in spec. If all this sounds way too confusing, just leave the memory ratio on auto and you'll be fine.
 
I'm going to be using a Giga-Byte GA-8IG1000MK. I have some generic stick of PC2700 512MB. After reading all this, i'll probably get two sticks of Crucial 256mb PC3200 that i'll run in dual channel. Is that motherboard any good?
 
that's your best bet for now. the mobo from what I read is slightly above average depending on what you are planning on doing with it.
 
Corsair is good, especially the XMS series. There are others as good if not better, some of which might be cheaper.

Two sticks for dual channel is an excellent idea. That will nearly double your memory bandwidth.

What is your O/C goal and what CPU will you be using? With PC3200 RAM, once you get above 210 to 220 FSB or so, you run the chance of having to fall back to the 5:4 ratio. If you are going for a big overclock, you might want to look into PC4000.
 
I used to run 2x512 value ddr 2700 w/ a 2.4 800 fsb (asus p4s800 mobo) It ran faster then the computer that I upgraded from but it didnt run at it's full potential. I'm in the upgrading ram and mobo, will be done this weekend I hope.


To answer the original question, yes it will run, just not as fast as it could
 
i'm going to be using a 2.8C with 2 Corsair 256mb PC3200. Motherboard is still GA-8IG1000MK. Stock heatsink for now, because i'm out of cash. hehe. Planning on the Thermaltake Spark 7+ shortly. What are my max OC capabilities with each heatsink combo. I'm using the Antec Aria 300W PS.
 
Depends on how high it goes on default vcore. Typically I recommend a better cooler above 3.2 gig, but if you can use low vcore, you might sneak it up a little higher. Just watch those temps. With better cooling you should be able to hit at least 3.4 gig. Use the 5:4 ratio.
 
I'm not understanding this 5:4 ratio stuff. is there somewhere in the BIOS i can physically change the ratio or is it a thing that just happens with sertain settings. I'm new to the ratio thing
 
It depends on the motherboard. Some allow cpu/memory ratio which increases the cpu speed without increasing memory speed or vice versa.
 
Memory Frequency For
for FSB(Front Side Bus) frequency=400MHz,
2.0 Memory Frequency = Host clock X 2.0.
2.66 Memory Frequency = Host clock X 2.66.
Auto Set Memory frequency by DRAM SPD data. (Default value)
for FSB(Front Side Bus) frequency=533MHz,
2.0 Memory Frequency = Host clock X 2.0.
2.5 Memory Frequency = Host clock X 2.5.
Auto Set Memory frequency by DRAM SPD data. (Default value)
for FSB(Front Side Bus) frequency=800MHz,
2.0 Memory Frequency = Host clock X 2.0.
1.6 Memory Frequency = Host clock X 1.6.
1.33 Memory Frequency = Host clock X 1.33.
Auto Set Memory frequency by DRAM SPD data. (Default value)

Memory Frequency (Mhz)
The values depend on CPU Host Frequency(Mhz) .

AGP/PCI/SRC Frequency (Mhz)
The values depend on Fixed AGP/PCI/SRC Frequency.


That is what i see in the BIOS for the GA-8IG1000MK
 
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