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800 FSB in a 400 FSB motherboard?

post #1 of 17
Thread Starter 
With memory and a motherboard, the board will only read the faster memory at what it's capable at.

So, a motherboard only capable of reading PC2100 memory, will read PC3200 at PC2100

Does it work the same way with CPU's and FSB?

For instance, will my motherboard, which is a 400mhz FSB, work with a CPU that is 800mhz FSB?
    
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post #2 of 17
Motherboards only have a *recommended* speed for memory. That means, if you put a ddr500 in a ddr400 board, it will go up to ddr500. Which is the reason you see ddr660 and such, because motherboards can go that high. You don't see any motherboards that says it uses ddr500, but it can handle it.

Anyway, I'm not sure about the CPU though. I was wondering this myself. Someone should reply soon enough though.
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post #3 of 17
Thread Starter 
Quote:
Originally Posted by kevin_tsoi2000
Motherboards only have a *recommended* speed for memory. That means, if you put a ddr500 in a ddr400 board, it will go up to ddr500. Which is the reason you see ddr660 and such, because motherboards can go that high. You don't see any motherboards that says it uses ddr500, but it can handle it.

Anyway, I'm not sure about the CPU though. I was wondering this myself. Someone should reply soon enough though.
I'm not sure if that's right. Everyone I've talked to has said that the memory will only be read at the speed that the board can read it at.

I've even gotten a direct response from FoxConn about my board and my PC2700 memory is only being read at PC2100. I'm sure it all depends on the boards too so...I dunno

I'm just wondering about CPU's....
    
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post #4 of 17
As far as I know a board that only supports a 400mhz CPU will not support a 533 or 800mhz CPU. The board is old therefore will not support the newer CPU's, I found this out the hard way when upgrading a compaq last year, the board supported 400mhz CPU's but would not support a 533 cpu.
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post #5 of 17
Often boards support higher frequency options via overclock. A supported 400MHz FSB board with supported 100MHz DRAM (100 X 4 = 400MHz effective) will almost always accept faster frequency DRAM but it will default to the mainboards support frequency.

So, lets say you wished to run 1:1 and overclock this 400MHz board. Then by installing higher speed DRAM you would be able to maintain the frequency without the use of a divider.

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post #6 of 17
Higher rated ram will work in a motherboad it will just be clocked down. In the case of using an 800FSB CPU in a 400FSB mobo it just wont work.
post #7 of 17
I think you guys missed the question in hand. He's simply asking if a 400mhz board will support a 800mhz CPU I.E. 3.0 prescott 1mbl2 800mhz buss speed. Well at least thats what I got.
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post #8 of 17
Quote:
Originally Posted by Adeoliver
I think you guys missed the question in hand. He's simply asking if a 400mhz board will support a 800mhz CPU I.E. 3.0 prescott 1mbl2 800mhz buss speed. Well at least thats what I got.
Yes this is what he is asking and i answered..simply a 400MHZ FSB BOARD will not work with an 800MHZ FSB CPU
post #9 of 17
Quote:
I'm sure it all depends on the boards too so...I dunno
I'm just wondering about CPU's....
Welll, that first part you're correct, it all depends on the motherboard.

That motherboard will not support an 800mhz fsb CPU nor 533mhz fsb CPU but it will be able to use DDR400/333 and downgrade it to DDR266.

The SiS 650 chipset is very limited.

Quote:
I've even gotten a direct response from FoxConn about my board and my PC2700 memory is only being read at PC2100.
I'm sure they responded: Because your CPU's fsb of 400mhz the memory will be downgraded to PC2100.
post #10 of 17
The main thing is that memory is a little more flexible because it's basically all the same arcitecture, just different speed, and it's a add-on basically. So a board can just slow it down to the speed it can use.

The CPU is the brain of the system, it's the main part and it does a lot more work than the RAM so there is less flexibility. The differences between a 400FSB CPU and a 800FSB CPU are more than just the speed also.

This why you see some boards that say they can take 533/800 FSB CPUs, where as others can only take 800/1066, and in many cases, they can only take certain CPUs in that FSB range. The chipset has to be able to recognize, and be able to communicate with that CPUs arcitecture.
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