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Question about a mobo's FSB multiplier.

Last response: in Motherboards
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May 11, 2008 7:38:08 PM

Hello,

I'm really into computer hardware just like everyone else here im pretty shore. :)  Ok Question is: Lets say you have a mobo rated at 800mhz FSB (Yea I know allot faster out there but trying keep this simple). Anyways even thou the mobo rated at 800mhz, the REAL FSB is 200mhz 4x (4x=multiplier). If the mobo is really has a 200mhz FSB then why is it rated at 800mhz? Dose multiplier mean there four times the data wires moving data (which would move four times the data but the data still moving from point A to point B at 200mhz or is the multiplier a like a amp for a FSB speeding it up by 4x? Im confused when it comes to this, I was hoping if one you guys that know your stuff can clear this up for me. Thanks for all the help and taking time to read this. :) 
May 11, 2008 8:56:56 PM

Because the full 4x number accurately represent the amount of data that can be moved. Some people do go by its 1x number, for simplicity's sake. Why does it matter how you call it? :p 
May 11, 2008 9:26:45 PM

thx, I was just wondering :) 
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May 11, 2008 9:56:36 PM

Base FSB frequency represents the physical clock rate.
Quadpumped (4x data rates) come from dual channel DDR(double data rate).
Difficult to explain without going into too much technical detail but it's 2 sets of wires (2 channels) leading into 2 registers accepting 2 words (64 binary bits) of data in every period of the clock signal (one in the high half and one in the low half).
It all means that in every period of the 200MHz FSB clock you get 4 transfers. So for a 200MHz FSB you get 2x(channels) 2x(data rate) 64bits (bus width) x 200 million clocks per second. That sums up to 6400 Mbytes/second maximum bandwidth.
a c 96 V Motherboard
May 11, 2008 9:56:49 PM

Ok, history lesson time.

Back in the olden days (P3 and below) the bus moved at 100MHz. This was also the amount of data that could be moved, as we could only send 1bit of data for each clock cycle. Your CPU might run at 700MHz (100MHz x 7 cpu multiplier.), but the connection to the northbridge would be 100Mb. (thats bits, not bytes.)

When the P4 came out, Intel started "quad pumping" the FSB. Basically, they found a way to send 4 bits per clock cycle. In this case your CPU might be running at 2GHz (100MHz x 20 cpu multiplier) but your FSB is now EFFECTIVELY 400Mb. The clock speed didn't actually change, but you can move more data through it.

You need to know the actual bus speed, as thats the one that the CPU clock is based off of. Lets look at a chip.

http://www.firingsquad.com/hardware/intel_pentium_4_3.4...

Quote:
Thus, it should come as little surprise that the latest flagship in Intel’s Extreme Edition family is a simple tweak of the 3.4GHz part that came before it. Rather than employing a 200MHz front side bus (quad-pumped, if you remember the original terminology, to run at 800MHz) and a hardwired 17x clock multiplier, the new chip uses a 266MHz bus (quad-pumped to 1066MHz) and a 13x multiplier.


All you have to do is do the math. If you have a chip that runs at 3.46GHz, and you try using the 1066MHz effective FSB, you'd get a multiplier of 3.25, which doesn't exist. If you divide 3460 by 266 however, you get the multiplier mentioned in the article.
May 11, 2008 10:04:59 PM

thank you learned allot from you guys:p 
!