Processor And Motherboard FSB Frequencies Must Match?

Posted on 2003-03-01
Medium Priority
Last Modified: 2013-12-10
Hey guys,

   I have a P4 2A GHz processor (2.0 GHz). The bus speed on the processor is 400 MHz. I also have a motherboard, but the bus speed on the motherboard is 533 MHz. Well, I put the processor into the motherboard and it worked. Frequently when I turn the computer on, though, I get an error message at the BIOS saying "no CPU installed". Is this due to the mismatch in the bus frequencies? Would I need a motherboard with 400 MHz FSB? Could this mismatch possibly have damaged anything? Also, when I go into the BIOS settings, it says the CPU hung due to an incorrect frequency multiple, or something of the sort. So basically my question is, do the CPU and motherboard FSB frequencies have to match? Thanks!
Question by:Noose215
LVL 32

Accepted Solution

jhance earned 60 total points
ID: 8053393
You should not run a P4 designed for 400 FSB at 533 FSB.  You'll get messed up operation since the P4 is not designed to permit arbitrary setting of the clock speed, multiplier, and FSB rate.

Setup your motherboard for 20X and 100MHz bus. This will get you the desired 2.0GHz (20 x 100MHz) and also 400 MHz FSB (5:1 clock/FSB ratio).

You MAY be able to play with the bus settings and get faster performance out of it but chances are your CPU is locked at 20X.  Most P4 chips are like this.

Expert Comment

ID: 8067122
Hi Noose215,
  The fault is because of this mismatch. It tends to overclock a CPU. But you could change the FSB setting from the motherboard by shorting the correct jumpers. Refer to manual or check the net. You must use Ur 2.0 GHz at 400MHz FSB. But 100x20 is the multiplier cause P4s actually have a QPR 100MHz system bus,; ie the 100MHz bus is pumped 4 times every machine cycle. Just like DDR, there's Quad Pumping Rate. I Also agree with jhance's points.


Expert Comment

ID: 8067155
Another thing,


 DDR -> Double Data Read, (AMD Style)
 QPR -> Quadriple Pumping Rate, (Intel Style)

Do not confuse between DDR-SDRAM & QPR. There is nothing like QPR-RAM as such. Thats why Intel originally recommended using RDRAM& not DDR SDRAm/SDRAMs on P4s.

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Expert Comment

ID: 8080114
additional note
what you see at FSB is actually mainboard clock, not CPU speed. CPU clock is defined by the bigger number. Clock is not the same as speed.
nowadays, FSB is mismarketed as Double Data Rate and Quadruple data rate. The true FSB is divided by 4 in Intel, and divided by 2 in AMD. So, 133/166 in AthlonXP, 100 in Duron, and 100/133 in P4. That's the true clock.

Memory clock is different, and must be set equal or less than your memory spec. e.g DDR333 must be set as 166 or less. It's called asynchronous memory.

A correction,
1. DDR stands for Double Data "Rate", not "Read". It's different because Intel uses "Read" as it reads 4 bits at 1 clock, while AMD uses "Rate" as AMD transmit twice in 1 clock in 1 bit each.
2. Intel WAS recommended RDRAM because RDRAM was the only memory with high bandwidth but also high latency. The first thing needed is bandwidth. Imagine that RDRAM is an urban street with 4 lanes and DDR is a highway with 2 lanes. DDR has much higher speed than RDRAM, but also much lower bandwidth than RDRAM. P4 is a hungry monster it doesn't need RAM quality, it needs bandwidth, as it reads 4 bit at once, but only once in 1 clock, at which AMD needs for speed and not bandwidth because it reads twice in one clock but only 1 bit each.
Now, with Dual DDR configuration DDR can kill RDRAM because Intel has provided P4 with enough bandwidth from low bandwidth DDR, but also added with DDR speed. So, let's say that DDR400 is about the same as RDRAM PC800 bandwidth, but with A LOT more speed.
Another note, is that Intel was using Dual channel RDRAM, so, to compete with Dual Channel RDRAM PC800 "bandwidth wise" you need Dual Channel DDR400. But actually, Dual DDR333 has about only a little less result with Dual PC800 because it cover it's weakness with its speed, and Dual DDR400 will exceeds Dual PC800.
So, P4 needs bandwidth, but Athlon needs speed. P4 doesn't need speed, and Athlon doesn't need bandwidth. They play on different field.

Expert Comment

ID: 8086740
Thanx prd00,
  Tat was a lot of techie info, a bit more than needed actually. But it all makes sense & is correct.

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by:Glen A.
ID: 9756173
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:

Answered by: jhance

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