FSB strap to NorthBridge so confused

[contra]

Does this : (posted by an ocuk forum legend cant remember the name)

FSB Strap does two important things:

* Offers different memory dividers
* Changes the latency of the Northbridge (tRD)

I'm finding the overclocked computer is running loads faster after manually setting the FSB strap to 200 and selecting the 2:1 divider, you will need pretty fast memory to select the latter.

If you select the lower FSB straps (200/266) while running a very high FSB you may need to give the northbridge some extra juice (vNB) to keep everything stable


Confilt with This : (written by some Tony guy)
FSB Strap for noobs.
Here it goes.

Your north bridge has an internal clock speed and latencies just like your CPU and memory. The FSB of your north bridge can be found by dividing your original CPU multiplier by your set CPU multiplier and then multiplying by your FSB.

So if you are running a E6600 (266 * 9) at 400Mhz x 8 your NB FSB is:

(9 / 8) x 400 = 450Mhz FSB (1800Mhz Total)

Just like your memory may be able to run at 4-4-4-12 at 1000Mhz but needs to run at 5-5-5-15 at 1200Mhz, your north bridge has a series of latencies which it must adjust in order to maintain stability at its FSB. These latencies seem to play a far more significant role in system performance than memory latencies.

Intel has predefined specific latencies at specific NB FSB speeds. They are referred to as straps. There is a strap for when the NB FSB is 1066Mhz and under, 1333Mhz FSB and under, 1600Mhz FSB and under, ect. When you go from the 1066Mhz FSB strap to the 1333Mhz FSB strap, the north bridge's internal latencies loosen to allow for greater stability.

ASUS has redefined the NB strap so that the 1333Mhz FSB strap does not come into effect until 401Mhz FSB (1604Mhz). Other perimeters of straps are someone unknown.

Tony, the guy who pretty much figured all this out and he works for OCZ. He is now a lobbyist trying to get ASUS and other major motherboard manufacturers to give the end user the control of when straps start.

There are 2 ways to beat the NB strap:

1. Boot to windows in the 1066Mhz strap and then use Clockgen to increase your CPU's FSB. You can then get to a much higher FSB while maintaining the 1066Mhz strap simply because the BIOS does not adjust the north bridge's latencies in real time.
2. Get a X6800 or QX6700 (or even a ES chip). To the north bridge, you are always at a default multiplier with a Extreme Edition processor. This allows you to set a much lower or higher multiplier without the NB FSB being effected.

So lower fsb strap means faster NB ? so so confused

 

[contra]

Answered my own question:

Essentially, the NB has its own expected, native clock frequency. Run it faster than that (as you crank up the FSB) and you hit some interesting performance changes depending how your northbridge changes its own internal reference clock.

It was more of an issue with the P965 chipset, the current P35, P45, X38, and X48 chipsets seem to benefit less from NB strap tweaking as MB makers have larger sorted this out, plus they also handle very high front side bus speeds much better than P965 does.

Generally, let your MB handle the NB strap now-- at least that's what I can tell.

And lower CPU multipliers result in faster NB speeds - never knew that

 

[Big.Wayne]

posted by an ocuk forum legend cant remember the name

Thanks! that's a classic Oxymoron btw!

So lower fsb strap means faster NB ? so so confused

I know how you feel, I was the same when trying to finally get my head around ye old northbridge but if you keep at it then you get that breakthrough moment when the penny drops!

Just to clear up your last point, a lower FSB strap will result in a lower tRD setting which seems to equate to a more snappy system. As the strap gets loosened upwards (266/333/400) the BIOS also loosens the tRD setting. This was more important on older motherboard/chipsets that didn't allow to to specifically adjust the northbridge straps or indeed the northbridges tRD.

The *strap* name itself doesn't help the end user understand any better but for all intent and purposes as I understand it there are no differences between the strap and something like SPD settings from memory, depending what MHz you are running there are a list of pre-determined timings associated with it, with memory you find the timings are lower when running lower speeds and looser when running fast speeds i.e a stick of DDR PC3200 may run at 3-3-3-12 when running at 200MHz but lower 2-2-2-6 timings when running just 133MHz, in effect the Northbridge strap acts much the same way . . .

And lower [than default/stock] CPU multipliers result in faster NB[CC] speeds - never knew that

Fixed!

That was a real eye opener for me also, once you understand that and the increased strain to the northbridge chip you can have a bit more fun when overclocking . . . you also start looking more closely at 3rd party Northbridge cooling and the E8400 seems a better high FSB overclocking prospect than say the E8600!