Noob question regarding FSB speeds.

[manowar]

Hi guys,

I have the Nvidia 680i SLI board, and a Core 2 Duo 2.4Ghz E6600 (OC'ed to 3Ghz).

Now, apparently, it does 1066/1333Mhz FSB.

Today, I cranked my FSB settings up in the BIOS to 1500Mhz, just out of curiosity (I've successfully been running my PC overclocked at 3Ghz until now). Which now means I'm roughly running at 3.3Ghz (FSB 375Mhz x 9 (multiplier) = 3.3Ghz.

Now, I'm getting a little confused with myself. If my board can do a max of 1333Mhz FSB, and my CPU FSB is 1500Mhz, does that mean my boards creating a bit of a bottle neck? A CPU running at 1500Mhz on a board capable of doing a max of 1333Mhz FSB?

Also, should I be doing anything with the multiplier? It's currently set at its default (9), but with 1500 OC'ed FSB, should I be lowering it?

Can someone please put me out of my misery and explain? Cheers guys.

 

[gurusan]

the 1066/1333 are just ratings for stock CPU speeds.

You have overclocked both the CPU and FSB, the FSB is now running at 1500mhz.....there's no bottleneck.

And there's no need to lower the multiplier for now...

 

[manowar]

Thanks gurusan.

So, for instance. If I bought say a CPU which had a stock FSB of say 2000Mhz, and put it into my current board, would it not work because stock speeds are set at 1066/1333Mhz? Or would it clock the CPU down to 1066/1333?

 

[gurusan]

Thanks gurusan.

So, for instance. If I bought say a CPU which had a stock FSB of say 2000Mhz, and put it into my current board, would it not work because stock speeds are set at 1066/1333Mhz? Or would it clock the CPU down to 1066/1333?

Well, there are no 2000mhz FSB cpus....

However, there are 1600mhz CPUs coming out soon....and remember that intel runs QDR (quad fsb, so 1600mhz = 400 real fsb speed)

So, if your motherboard supports the actual CPU and you stuck in the 1600mhz FSB cpu, your motherboard would either:

A) automatically overclock itself to 400mhz (1600 effective)
B) run at the motherboards stock 266 or 333fsb...resulting in a downclocked cpu (but you could just raise the FSB manually)

 

[manowar]

Yeah, I understand. The "2000Mhz" was just an example.

So, basically I'm ok running at 1500Mhz FSB?

I'm still a little unclear, though. I've put the CPU FSB settings to 1500Mhz, (3.3Ghz) are you saying that the boards FSB basically automatically increments to 1500Mhz as well? So there's no bottlenecking?

My understanding is this:

1. The CPU has a FSB, in this case a stock of 1066Mhz
2. The motherboard has stock FSB 1066 and 1333Mhz

If you increase the CPU FSB to 1500Mhz, (3.3Ghz), effectively, if your board permits "unlinked" abilities, it'll also set its own FSB to 1500Mhz, or there abouts?

Thanks for you help

 

[gurusan]

You're thinking about it the wrong way...

Treat the CPU and motherboard fsb as the same thing. They aren't 2 different things that are linked or unlinked.

CPU speed = FSB * multiplier

That's all you really need to know.

 

[manowar]

Thanks, Gurusan. So in other words, the CPU FSB is 1500Mhz and forget about the whole 1066/1333Mhz thing?

This leads me to the next thing. I have PC2-8500 (1066Mhz FSB) RAM (4Gb). It's currently running at 1066Mhz (unlinked), do I need to lower/increase this at all in conjunction with my oc'ed CPU settings?

 

[gurusan]

Just call it FSB, not CPU or MB fsb to avoid confusion.

And if your ram is unlinked then no there's no need to change the ram multiplier...1066mhz is quite fast enough.

 

[manowar]

Just call it FSB, not CPU or MB fsb to avoid confusion.

And if your ram is unlinked then no there's no need to change the ram multiplier...1066mhz is quite fast enough.

Thanks for all your help, gurusan.

Can you explain, briefly, why the RAM is ok at 1066Mhz and why it has to be unlinked?

 

[gurusan]

***CLIFF NOTES***
-Since you have your memory unlinked and it's also already running at a fast speed, there's no real need to worry about it....just leave it at unlinked

**************

The ram works on a FSB multiplier just like the CPU...and it's rated at double speed so it's "real" speed is 533mhz while it's effective rate is 1066mhz...hence the term DDR (double data rate)

If your FSB is 333mhz stock that means your ram is running at a 1.6x multiplier (1.6 x 333 = 533mhz, or 1066 effective)

On most motherboards as you increase the FSB, the RAM speed will increase just like the CPU since they are both on multipliers.

So usually you are overclocking your ram (i.e. 333mhz--->350mhz means you would have overclocked your ram to 560mhz[350*1.6], or 1120mhz) But since you have your ram set to "unlinked"..it doesn't scale with the FSB.

For motherboards that don't have the unlinked option you can knock down the RAM multiplier if the PC becomes unstable in order to eliminate the RAM overclock (i.e. reduce multi to 1.25x so it runs at 438mhz or 875 effective)