What exactly is front side bus speed?

[kj1212]

You guys have been so helpful to me already in building my first system, and the inevitable troubleshooting afterwards that I though I might try to learn some more! My system has the following:

P4 2.4G 533FSB
Asus P4C-800 Deluxe mobo
2 sticks Corsair XMS pc3200

I have an identical motherboard, and everything else I need for another system except for the chip and ram. I'm thinking about a P4 2.8G with hyperthreading, because I've heard nothing but good things about it, but I'd like to know what the difference is between it and the regular 2.8 w/o hyperthreading. Would the PC3200 ram work well with the 800fsb, or would I need better ram. I have no clue of the workings between the chip and ram. If anybody has a second to educate me, I'd appreciate it!! Thanks again.

[DanGrease]

What is Front Side Bus (FSB)?
Well to but it in my own words I would say its the speed (in MHz) the processor takes to send information. More speed, better performance. Comparing the Pentium 4's with 533Mhz FSB and the ones with 800MHz FSB the one with 800 outperforms the other simply because it sends information faster so it operates faster. Currently the processor considered to be the most powerful is the G5 from Macintosh. It has a FSB of 1 GHz. HTH's

dan

[krohnjw]

I think a better analogy is that the FSB is like the highway between the CPU, main memory, and elsewhere in the computer. The higher the "Frequency" the more "lanes" the highway has. The more lanes the highway has the more data it can transfer at one time theorhetically.

[kj1212]

Wouldn't the memory, with a 400mhz speed, bottleneck that data from the cpu?

**Disclaimer*** I'm completely clueless on this stuff

Thanks again!!

[Gait_Keeper]

great link Dan!!!!!!!!!!!!!!!!!

[Darthgary]

Well a good example is comparring the AMD Athlon XP to the P4.

The Athlon Sends its information to the chipset via DDR (Double Data Rate) at 200X2 which = 400 Mhz. The P4 sends its data QDR 200X4 (Quadruple data rate) which = 800 Mhz.

The Athlon XP Barton sends data at 9 clock cycles per second and the P4 sends it at 6, it is like a highway, the P4 has a 4 lane highway and the Athlon XP has a 2 lane highway, the P4 does less work per clock cycle so it has plenty of room for more cars thus higher frequency, the Athlon XP does more work per clock cycle but sends the data on a smaller highway which is why the Athlon can only go so high in frequency before releasing another core with a wider 2 lane highway to support bigger cars - Higher clock cycle.

FSB overclocking will overclock all your components unless its locked down, most modern boards have the PCI/Parelel HDD Bus's and the AGP port locked at its default FSB. FSB X Multiplier = Frequency, this applyes to every thing like John Prophet
mentioned. Note that if your AGP port is overclocked, this does not mean your video card is, this only means that the information flow from the port to the chipset or if using fast writes port to CPU would be speeded up, most video cards will not efficiently benifit from a overclocked AGP Port.

[Dmack_901]

but he is right, right? You computer is only as fast as your slowest component.

[John Prophet]

The frontside bus is sort of "the speed of the motherboard" in a certain sense....then you mulitply that by the "multiplier" and you get the speed of the cpu....in other words the cpu runs at super high speeds compared to the fsb and the memory etc. So much so that modern processors are sitting idle waiting for something to do, lol.

Memory IS a bottleneck but then again so is the hard drive....depends on what application is running.

The fsb runs thru a "divider" for the pci bus to keep the pci bus round about 33mhz. And some pci busses have "locks" so that no matter what the fsb is, the pci stays ay 33mhz. But on most boards..when you over clock the fsb you also over clock the pci.

Back when all these standards were being made, a 66mhz fsb was the standard..it lasted a long time...so things sort of normalized around that.

The pci bus was half the fsb 66/2=33

When the agp bus first came out it ran at the full fsb....or 66mhz.

Then they came out with 2x AGP...so that was 133 (rounded)mhz..then 4x at 266mhz

All of these numbers come into play when overclocking also..since they are all related.

in an old system...say a P1@66mhz....if you overclocked to 68mhz....that means you also overclocked your agp video card to 137mhz and RAM to 68mhz and your pci cards to 34mhz.

All that comes into play because at some point with overclocking..one of those components will decide it doesnt want to run that fast....for instance it could be your modem deciding it doesnt like the 37mhz pci clock.

For instance with the classic old intel "BX" chipset..the agp and fsb were sort of "locked" so when you overclocked the fsb you also overclocked the agp...and usually the video card revolted, lol.

That is why now with the modern boards you have allllllllllll kinds of options to help with overclocking. All sorts of "dividers" to keep the pci bu within sane speeds...or "locks" to keep it at 33mhz. You also have tons of memory settings now as well as agp settings.

So now its really tweakable to the point where you almost have 3 or 4 different little overclocking situations in a pc at once.

CPU overclocking
video card "
RAM "
PCI bus "

You also see lots of "asynchronous" settings now. For instance if you have a athlon running at 133 fsb but you only had pc100 ram..then you run the fsb at 133 and the ram at 100...or vice versa...if you have a duron at 100fsb you can run your pc133 ram at 133mhz to get the full benefit of it.

Primer/End

JP

[iseeu_3]

i think that the highest fsb speed now is the amd 64 fx-51 at like 1600mhz! i thought that was a typo on this web site but then i read it again it pcworld. but yes, the cpu is ALWAYS the fastest component on the mobo (in most cases i guess).

<shad>

[iseeu_3]

oh yeah, this should help on the hypterthreading question:

http://www6.tomshardware.com/cpu/20021227/