FSB?

[Guest]

Can anyone explain what this FSB is and what relationship to the motherboard it has? It other words, whats it for whats it do.

-- Computers run on smoke! If you let the smoke out they wont work anymore.. --

 

[mpjesse]

FSB stands for Front Side Bus. It's speed is the speed at which the northbridge (or main part of the chipset) talks to other components like memory, AGP interface, PCI interface, and southbridge (typically the hard drive controller). It's also the biggest bottleneck in the PC system- while the processor is running at 1Ghz, the rest of the system is operating at 133 or 100mhz.

The higher the FSB the more performance. Right now, the "official" fastest FSB is 133mhz. But, many people have reached speeds of 166mhz and beyond by overclocking. My FSB runs at 140mhz. Understand?

-MP Jesse

"Signatures Still Suck"

 

[Guest]

Yep understood thanks a bunch for clering that up. One more question i have though is how can retailers say that there selling a system with a 266 FSB?

-- Computers run on smoke! If you let the smoke out they wont work anymore.. --

 

[slvr_phoenix]

That's mostly correct, but the AGP and the PCI (and consequently the ISA) are set to run at specific speeds. I believe AGP is at 66MHz and PCI is at 33MHz. (I could though be totally wrong on these numbers as I'm pulling them from memory.) And I think ISA is half of PCI. [shrug]

So in actuality, the FSB of the motherboard has no impact on the bus speeds AGP and PCI. (Overclocking not being accounted for because that complicates matters.) As such, it isn't really the bottleneck at all. The real bottleneck is the architecture used for things like AGP and PCI.

So, for the most part, the FSB is just for the processor to transfer data faster to and from the memory and to the north bridge. And this is why it's good practice to use memory that has the same (or faster) FSB as the CPU, otherwise the memory will end up being a bottleneck.

If the opposite of pro is con, what is the opposite of productivity? Ground first.

 

[slvr_phoenix]

The 266MHz FSB is a marketting myth that surrounds Athlons. The Athlon runs a double-pumped 133MHz FSB. (And before that a double-pumped 100Mhz FSB.) The FSB is still technically 133Mhz. It's just the way that the chip uses it internally that is different.

Marketting though, in it's ever infinite wisdom, started calling it a 266MHz FSB. (Probably because they couldn't understand what a double-pumped bus even was themselves.) And so a fallicy was born.

If the opposite of pro is con, what is the opposite of productivity? Ground first.

 

[Kelledin]

A lot of systems run on a DDR (Double Data Rate) FSB--that is, they transfer data twice per clock cycle. Even though the FSB is still running at, say, 133MHz, it's transferring twice the amount of data, achieving about the same effect as having the bus clock running at 266MHz. So salespeople can get away with saying a system has an "effective" 266MHz FSB. It's not really deception so much as putting it in terms where people can better understand the benefits.

Kelledin

"/join #hackerz. See the Web. DoS interesting people."

 

[slvr_phoenix]

I would agree with you that it isn't deception if DDR systems ran twice as fast.

They don't.

In fact, you can find SDR systems that run faster than DDR systems using the same CPU, cards, etc. (The only difference being the motherboard and the memory sticks.)

DDR is as much of a hyped myth as 266MHz FSBs.

If the opposite of pro is con, what is the opposite of productivity? Ground first.

 

[Kelledin]

tr00, tr00...although if the FSB really was 266MHz, it still wouldn't be twice as fast. Claiming the entire system is twice as fast because of a DDR bus would be deception, but simply calling 133MHz DDR "266MHz" is just an issue of technical semantics.

Kelledin

"/join #hackerz. See the Web. DoS interesting people."

 

[slvr_phoenix]

Okay, you got me there, the whole system shouldn't be twice as fast just because it's 266MHz.

However, the front side bus refers not to the internal speed of the CPU or of the memory. It refers to the interface with the northbridge/chipset and the speed of that bus.

Putting in a double-pumped CPU or a double-pumped memory stick (or even both) does not a 266MHz FSB system make.

So long as the FSB is still only 133MHz, the system is still only a 133MHz FSB system. So calling it a 266MHz FSB system when it really isn't is a lie.

If the opposite of pro is con, what is the opposite of productivity? Ground first.

 

[mpjesse]

Well, DDR might not double the speed- but it does double the bandwidth. So, the bandwidth of a DDR system is comparable to a 266mhz FSB (non-DDR). That's a good arguement on why it isn't a lie. Isn't it?

-MP Jesse

"Signatures Still Suck"

 

[mpjesse]

No, that's all correct. Notice I didn't say that 133mhz was the speed at which the AGP and PCI bus talk to the cards or components. However, 133mhz is the speed at which the northbridge talks to the AGP & PCI controllers. AGP talks to the component at 66mhz, PCI at 33mhz, and ISA 16mhz.

-MP Jesse

"Signatures Still Suck"

 

[phsstpok]

. AGP talks to the component at 66mhz, PCI at 33mhz, and ISA 16mhz.

Those are the intended speeds of the various buses except ISA is spec'd at 8 mhz.

To confuse matters here, most motherboards use relative frequencies. AGP is usually 1/2 or 2/3 of FSB speed depending on whether the FSB is set to 133 mhz or 100 mhz. Likewise, PCI is 1/4 or 1/3 of FSB speed. ISA is 1/4 of PCI speed.

(Sorry to correct you while you are on a roll)

<P ID="edit"><FONT SIZE=-1><EM>Edited by phsstpok on 06/15/01 00:53 AM.</EM></FONT></P>

 

[mpjesse]

My bad.. confused the fact that ISA is a 16bit bus on a 8mhz clock speed, not 16mhz =)

-MP Jesse

"Signatures Still Suck"

 

[slvr_phoenix]

While I agree that the theoretical bandwidth of a DDR system is doubled, it's still not a true 266MHz bus. The bus is still 133MHz, just accessed twice per cycle instead of only once. A 100MHz FSB chip with a multiplier of 8 and a 133MHz FSB chip with a multiplier of 6 are both called 800MHz chips. Yet the FSB's in each are clearly different.

The same is true of DDR. The pumping is a multiplier. The FSB is still 133MHz or 100MHz. If I called a P3-800MHz CPU an 800MHz FSB with a multiplier of 1, you'd laugh your head off, right? Well, double-rate is the exact same scenario.

And aren't there 8-bit ISA cards too? I seem to remember a really old system having what looked like an ISA card cut in half...

If the opposite of pro is con, what is the opposite of productivity? Ground first.

 

[Pettytheft]

Would it be possible to split the PCI from the FSB? From what I understand the problem is when raising the FSB you need to change the divider for the PCI bus. So why not just lock the PCI bus and with the AGP at twice the PCI 33mhz speed. It just seems to make more sense than to continue to have the PCI scale with the FSB.

Is this possible?

Blah, Blah Blahh, Blahh, blahh blah blahh, blah blah.

 

[Sojourn]

The bandwidth of a DDR clock isn't "theoretically" twice that of a SDR clock, it _is_ twice that of its SDR counterpart. Also, don't confuse bus clock multipliers as used in CPU's with DDR or QDR technology. A CPU running at 800MHz is running at 800MHz, whether its bus is running at 133MHz or 100MHz.

The marketing device of labeling a 133MHz double pumped clock as 266MHz is a justifiable necessity. It performs exacttly the same as its 266MHz SDR equivilant (except that it doesn't consume as much power.) Also, although the clock is running at 133MHz, it is delivering data bits at a rate of 266MHz, so labeling it as 266MHz isn't even a boldfaced lie. But the real reason they label it like that is that if you were to put a 100MHz DDR component next to a 133MHz SDR component and ask the average user to pick one, he'd pick the 133MHz component because the average user doesn't know what DDR means.

Also note that the DDR SDRAM memory industry has taken truth in labeling a step farther and begun labeling its memory by its bandwidth performance rather than its clock.

-= This is our wading pool.
Stop pissing in it. =-

 

[Sojourn]

Intel's new chipsets allow you to change the clock multiplier (or in this case, divider) for the PCI/AGP busses. This should allow for some incredible FSB overclocking, since it is usually the peripherals that don't like to be run very far out of spec.

-= This is our wading pool.
Stop pissing in it. =-

 

[mpjesse]

Yeah- 8 bit ISA was back in the 286/386 days. Remember MCA? Micro Channel Architecture- developed by IBM. It was advanced for it's time, but somehow never made it to the standard. ISA won.

-MP Jesse

"Signatures Still Suck"

 

[Pettytheft]

MCA got beat out because IBM tried to pull a Rambus on the industry. It was superior to anything else but they wanted all the IBM clones to pay royalties to IBM. The rest of the industry pulled together, copied MCA, named it ISA and IBM had to give up due to the fact that they were the minority compared to all the clones. Funny thing is that MCA was still superior to ISA.

Blah, Blah Blahh, Blahh, blahh blah blahh, blah blah.