Host Bus and FSB

[Guest]

Dear all,

AMD Atholon CPU always calim that the cay have System Bus up to 266Mhz. However, is it the theorectical value? In the motherboards, I don't seen any FSB have such a high value? Only the standard 100Mhz, 133Mhz. Besides, I heard that even you overclock the FSB/System Bus of the motherboard, it is impossible to set as high as 160Mhz with a stable sysem. Then, what is the value of 266Mhz?
I wonder wether it means the internal bus speed in the CPU? or just the host bus between the sockets and the system bus/memory bus?
Best regards,
Teres

 

[somerandomguy]

It is a 133Mhz Double Data Rate (DDR) bus, which means that while it has a clock speed of 133Mhz, it’s effectively 266Mhz when compared to a Single Data Rate (SDR) bus.
The 400Mhz RD RAM is actually a quad pumped 100Mhz Bus, in case you were wondering about that too.

"Ignorance is bliss, but I tend to get screwed over."

 

[Raystonn]

For an Athlon system, the FSB is single-pumped off the external clock. The external clock is 133MHz. This offers a 133MHz FSB. With DDR SDRAM transmitting twice per clock, it is the equivolent of a 266MHz FSB.

For a Pentium 4 system, the FSB is quad-pumped off the external clock. The external clock is 100MHz. This offers a 400MHz FSB. With DRDRAM transmitting twice per clock, it is the equivolent of an 800MHz FSB.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[LoveGuRu]

now what makes you think im posting on the subject?

<font color=green>
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*K.I.S.S*
*(k)eep (I)t (S)imple (S)tupid*
*******
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[Raystonn]

Would you mind too much posting this stuff in one of the other THG forums? It still increases your post count for all forums, and it saves us the trouble of having to read all these threads when no real information has been added.

Thank you.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[LoveGuRu]

relax man..just didnt want to hug a single thread..

<font color=green>
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*K.I.S.S*
*(k)eep (I)t (S)imple (S)tupid*
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[killall]

uhm, no... you dont need ddr to run at 266, it runs at 266 internally anyway... the p4 on the other hand runs at 400... making it apparently faster clock for clock (you see this is not the case, though the 2ghz is the fastest chip out)

if in doubt blame microsoft...

 

[Raystonn]

"you dont need ddr to run at 266, it runs at 266 internally anyway"

No, Athlon systems running with PC2100 DDR SDRAM memory have a 133MHz FSB. The memory is specced at 266MHz because it performs 2 clocks for every FSB clock. (Thus the name DDR.)

Athlon systems running with PC133 SDRAM memory also have the same 133MHz FSB. This memory performs the normal 1 clock for every FSB clock. (Thus it is SDR.)

Pentium 4 systems (with an i850 chipset) have a 100MHz external clock, a 400MHz FSB, and 800MHz DRDRAM memory. (They transfer 16-bits at a time, 2 bytes, thus the 1.6GB/s per channel figure.)

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[FatBurger]

If you want to raise your post count, go join the [H]ardOCP forums, and take Yahiko and Techie with you.

<font color=green>I post so you don't have to!
9/11 - RIP</font color=green>

 

[LoveGuRu]

couldnt help posting could you?

what are u 10 YO?

<font color=green>
*******
*K.I.S.S*
*(k)eep (I)t (S)imple (S)tupid*
*******
</font color=green>

 

[MeTaLrOcKeR]

I think he was refferignt o this Raystonn....look at what us aid about the Athlon and compare it to what u said about the P4..

"For an Athlon system, the FSB is SINGLE-PUMPED off the external clock. The external clock is 133MHz. This offers a 133MHz FSB. With DDR SDRAM transmitting twice per clock, it is the equivolent of a 266MHz FSB."

"For a Pentium 4 system, the FSB is QUAD-PUMPED off the external clock. The external clock is 100MHz. This offers a 400MHz FSB. With DRDRAM transmitting twice per clock, it is the equivolent of an 800MHz FSB."

This si what he was referrign to, not just the DDR ram.....you said the Athlon is SINGLE PUMPED off the external bus, when it is DOUBLE-PUMPED =) a little foul up my friends but its quite alright =)

-MeTaL RoCkEr
My <font color=red> Z28 </font color=red> can take your <font color=blue> P4 </font color=blue> off the line!

 

[somerandomguy]

RD RAM transmits twice per clock as well? I didn't know that.
DDR = At 133Mhz x 64 bit data path x 2 transmissions per clock = 2.1 Gigabytes per second
RD = At 100Mhz x Quad pumped x 32 bit data path x 2 transmissions per clock = 3.2 Gigabytes per second
but doesn't RD RAM have a 16 bit data path?
What exactly is quad pumped anyway?

"Ignorance is bliss, but I tend to get screwed over."

 

[Raystonn]

"you said the Athlon is SINGLE PUMPED off the external bus, when it is DOUBLE-PUMPED"

No, the FSB is single pumped off the external clock. When you set the external clock to 133MHz, the FSB is also set to 133MHz. On the Pentium 4, when you set the external clock to 100MHz, the FSB is set to 400MHz. An Athlon that makes use of DDR SDRAM still uses the same single-pumped FSB. That DDR memory transmits twice per clock. The memory is double-pumped off the speed of the FSB, but the FSB is not.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[Raystonn]

"RD RAM transmits twice per clock as well? I didn't know that."

Yes, it does.


"DDR = At 133Mhz x 64 bit data path x 2 transmissions per clock = 2.1 Gigabytes per second"

Yes, this is accurate.

"RD = At 100Mhz x Quad pumped x 32 bit data path x 2 transmissions per clock = 3.2 Gigabytes per second"

This is inaccurate. Current forms of RDRAM have a 16 bit data path. The i850 chipset provides for two of these channels. Thus:

External Clock = 100MHz
FSB = External Clock * 4 (quad-pumped) = 400MHz
RDRAM effective clock = FSB * 2 = 800MHz
RDRAM effective bandwidth per channel = RDRAM effective clock * width of RDRAM module (16-bits, a.k.a. 2 bytes) = 1.6GB/s
i850 total memory bandwidth = RDRAM effective bandwidth per channel * 2 (dual channels) = 3.2GB/s


"What exactly is quad pumped anyway?"

This means the FSB clocks 4 times every time it receives a single clock from the external clock on the motherboard.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[somerandomguy]

Thanks Raystonn, you’re very helpful and informative.

"Ignorance is bliss, but I tend to get screwed over."

 

[Matisaro]

Ray, dosent the athlon have a double pumped fsb all the time, regardless of if its dram or ddrram?

~Matisaro~
"The Cash Left In My Pocket,The BEST Benchmark"
~Tbird1.3@1.5~

 

[MeTaLrOcKeR]

Matisaro, this was the point that I was tryign to brign up......even on Early THG articles, about when the frist Athlon was released in Slot A form and 0.25 Micron...it had a 100MHz (200MHz DDR) Double-Pumped FSB....
I Still have a Motherboard box of the old Slot A ASUS K7M box, and right on it it says 200MHz FSB.....and we all know those boards use SD-RAM as DDR was not out yet...

Raystonn, are you saying that the whole world is wrong, INCLUDING AMD ??? On there webiste in the FAQ about the Athlon it states 'The AMD Athlon processor uses the EV6 Bus Protocol which is set at 100 or 133MHz (200 or 266MHz DDR) effectively)....
YES, SDRAM, in itserlf, cam ONLY transfer at 1 instruction per clock or whatever.....thats between the RAM - CHIPSET....
When the Chipset reads/writes to the CPU however it is talkignt o it in DDR, correct ? Hence 100 (200MHz DDR) or 133 (266MHz DDR)...

SDRAM: RAM - Chipset (Single-Pumped), Chipset - CPU (Double-Pumped)
DDRAM: RAM - Chipset (Double-Pumped), Chipset - CPU (Double-Pumped)

Is this right or what ?

Raystonn you do give very valid info all the time, but i honestly think you are a bit inaccurate, look at AMD FAQ on the AMD Athlon Processor on their website, and look at very EARLY Tom's articles about the Athlon.... =)

-MeTaL RoCkEr
My <font color=red> Z28 </font color=red> can take your <font color=blue> P4 </font color=blue> off the line!

 

[Matisaro]

Exactly what I wanted to say whithout getting in another tangle with ray ;-).

I found his little summary to be flawed in another respect, while he claimed the athlon did not have a double pumped fsb he maintained that the p4 had a 400mhz buss all the time(even with dram).

Well ray, are you wrong, or are we misunderstanding you?

~Matisaro~
"The Cash Left In My Pocket,The BEST Benchmark"
~Tbird1.3@1.5~

 

[MeTaLrOcKeR]

That also was something else I wanted to re-mark on......

This means with SDRAM on i845 the P4 is only single-pumped aswell...but we know that nto true becasue the way the DRAM communicate to the Chipset has nothing to do with how the Chipset communicate to the CPU via Host bridge correct ?
Well it IS simialr but they are 2 different ratio's.......otherwise if you think about it, how would we be able to use different memory types otherwise?
AND if i845 with SDRAM was only single-pumped, I think there would eb a MUCH GREATER performance hit than it already took......would you not agree Ray ??
Aswell with the Athlon, except when using DDR in this case u say the FSB IS Double-Pumped as opposed to being Single-Pumped with SDR....there'd be a MUCH greater performance Increase, insaid of an overall 15% when usign DDR over SDR....am i right or what ?!?

-MeTaL RoCkEr
My <font color=red> Z28 </font color=red> can take your <font color=blue> P4 </font color=blue> off the line!

 

[Raystonn]

The Athlon has a single-pumped FSB at all times. The actual operating speed of the FSB in relation to the external clock speed is how you measure this. On an Athlon the external clock is set to 133MHz. The FSB is 133MHz. It is therefore single-pumped. If you use DDR SDRAM, it transmits twice per clock, giving you a simulated 266MHz, but in reality still using a 133MHz clock.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[Raystonn]

"The AMD Athlon processor uses the EV6 Bus Protocol which is set at 100 or 133MHz (200 or 266MHz DDR) effectively)"

This is exactly what I am saying. The Athlon's FSB is set to the same clock as its external clock, 133MHz. It has a single-pumped FSB at all times. The actual operating speed of the FSB in relation to the external clock speed is how you measure this. On an Athlon the external clock is set to 133MHz. The FSB is 133MHz. It is therefore single-pumped. If you use DDR SDRAM, it transmits twice per clock, giving you a simulated 266MHz, but in reality still using a 133MHz clock.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[Raystonn]

"he claimed the athlon did not have a double pumped fsb"

It does not.


"he maintained that the p4 had a 400mhz buss all the time(even with dram)."

It does. The FSB does not change regardless of what memory you place in the system. It only changes when you modify the external clock. Do not confuse the FSB with the speed of your memory. The SDRAM (i845) chipset uses a 1/3 multiplier off the 400MHz FSB to transmit at 133MHz synchronously. The FSB of the Pentium 4 is still running at 400MHz.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[Matisaro]

I dont know ray, sounds a tad fishy, but I believe you untill I look it up tonight.

How does the p4 keep its 400mhz buss at all times, and does this give a performance advantage?

~Matisaro~
"The Cash Left In My Pocket,The BEST Benchmark"
~Tbird1.3@1.5~

 

[Raystonn]

"How does the p4 keep its 400mhz buss at all times"

The FSB is always quad-pumped off the external clock. This means for every 1 clock it receives, the FSB produces 4 clocks of its own. We could have simply gone with a 400MHz external clock, but the 100MHz clock is easier to work with for certain components. No matter what you plug into the other end, the FSB will continue operating at the same speed.


"does this give a performance advantage?"

For the i845 chipset it does not offer any further bandwidth than the memory provides, but it does offer reduced latency. The data is run over a 400MHz FSB and thus gets to the processor more quickly than if it had been run over a 133MHz FSB. Of course, for SDRAM this reduced latency does not offset the pitiful bandwidth that is provided.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[MeTaLrOcKeR]

Ray, Is till have to disagree......
How can AMD claim that there FSB is Double-Pumped if its not ?!? it doesnt add up....
Yes i know what your sayign about the external clock.....BUT
im talkign about how the Chipset communicates to the CPU.....it is 100/133 (200/266 DDR) is it not ?!?
not the Memory - Chipset.......that can only go as fast as the memory does....an hence with SDRAM, SINGLE-PUMPED to the chipset, and with DDRAM, DOUBLE-PUMPED to the Chipset, and than AGAIAN Double-Pumped to the processor due to the Athlon's Digital Alpha EV6 Bus Protocol....which does state that it's a double=pumped bus....i never sdaid its double-pumped from the memory controlelr to chipset...thats obviously only as fast as the memory is......

-MeTaL RoCkEr
My <font color=red> Z28 </font color=red> can take your <font color=blue> P4 </font color=blue> off the line!