FSB800 at 200MHz?

  • Thread starter Thread starter Ian
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Ian

I'm in the process of building a new system, looking at some of the ASUS boards
in the P4P800 series.
Just downloaded the pdf manual for the P4P800S SE which has a FSB of 800MHz
and can take DDR400 RAM.

Now my understanding is that the board runs at 800MHz to the CPU, and runs at
400MHz to the RAM, however on page 2-17 of the manual there is an FSB/CPU
table that states:

Front Side Bus FSB 800 = CPU External Frequency 200MHz.

Is this a typing error, why is the external frequency of the CPU only 200MHz,
wouldn't it be 800MHz.
I haven't built a new system from the ground up for a few years (only upgrades),
so I'm not totally up to speed with all the new stuff.

Cheers
Ian
 
Ian said:
I'm in the process of building a new system, looking at some of the ASUS boards
in the P4P800 series.
Just downloaded the pdf manual for the P4P800S SE which has a FSB of 800MHz
and can take DDR400 RAM.

Now my understanding is that the board runs at 800MHz to the CPU, and runs at
400MHz to the RAM, however on page 2-17 of the manual there is an FSB/CPU
table that states:

Front Side Bus FSB 800 = CPU External Frequency 200MHz.

Is this a typing error, why is the external frequency of the CPU only 200MHz,
wouldn't it be 800MHz.
I haven't built a new system from the ground up for a few years (only upgrades),
so I'm not totally up to speed with all the new stuff.
Click to expand...

The 800MHz FSB is derived from the 200MHz Memory (Obviously doubled for DDR,
which gives you the DDR400), then quad pumped to give 4x200 = 800. It's the
way Intel have done all of the P4s, my 1.7 is 400MHz FSB, 4x100, and the 533
generations of P4s were 4x133 (DDR266)

Somebody please correct me if I'm wrong here, but IIRC thats how it's
done.....
 
Phil said:
The 800MHz FSB is derived from the 200MHz Memory (Obviously doubled for DDR,
which gives you the DDR400), then quad pumped to give 4x200 = 800. It's the
way Intel have done all of the P4s, my 1.7 is 400MHz FSB, 4x100, and the 533
generations of P4s were 4x133 (DDR266)

Somebody please correct me if I'm wrong here, but IIRC thats how it's
done.....
Click to expand...

Yes.
But to clarify and confirm ....
200MHz CPU clock
Uses DDR ram, so doubles 200 to DDR400 (or PC3200)
But the RAM is arranged in pairs - you must put two at a time in to use
the 800MHz bandwidth.

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The computer's FSB is 200 MHz
The P4 CPU runs INTERNALLY at 4 x the FSB = 800MHz.
The DDR (Double Data Rate) runs at double the FSB = 400 MHz.
 
=|[ Gareth Jones's ]|= said:
Phil said:
The 800MHz FSB is derived from the 200MHz Memory (Obviously doubled for DDR,
which gives you the DDR400), then quad pumped to give 4x200 = 800. It's the
way Intel have done all of the P4s, my 1.7 is 400MHz FSB, 4x100, and the 533
generations of P4s were 4x133 (DDR266)

Somebody please correct me if I'm wrong here, but IIRC thats how it's
done.....
Click to expand...

Yes.
But to clarify and confirm ....
200MHz CPU clock
Uses DDR ram, so doubles 200 to DDR400 (or PC3200)
But the RAM is arranged in pairs - you must put two at a time in to use
the 800MHz bandwidth.
Click to expand...

P4 has quad 32bit wide pumps on its front side bus
they connect to 64bit wide ddr channels
RDRAM did it another way,

i dont remember
 
DaveW said:
The computer's FSB is 200 MHz
The P4 CPU runs INTERNALLY at 4 x the FSB = 800MHz.
The DDR (Double Data Rate) runs at double the FSB = 400 MHz.
Click to expand...

The last system I built from the ground up was an AMD K6-2/400
with a Chaintech motherboard, the board ran at 100MHz and the jumpers
for the clock multiplier were set to 4 (to get 4 x 100 = 400MHz internal CPU).
So with that analogy, I would have thought that a board that has an FSB of 800MHz
would run at 800MHz with a clock multiplier of say 3.75 to get the CPU's internal rate
to 3000MHz (3GHz).
So do AMD and Intel motherboards differ in this regard.

Cheers
Ian
 
Internally they run 4xFSB, so that measn to get 3.0GHz (like mine is) you
run 200MHz x 4 x 15 multiplier.

..au:
 
Guys, thanks for all your input.
Seems I'm not up to speed with all the new technology, didn't know anything about
double or quad pumping, which is why I couldn't understand the 800MHz FSB stuff.
After spending my lunch break searching Google, I found the following site that also
helped clear things up.

http://www.directron.com/fsbguide.html

Cheers
Ian
 
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