finding max FSB

[NickFas]

how do i find the maximum fsb for my particular motherboard. I saw thi s on overclock.net and i was curious what he meant by the following sentence.

4) Raise your memory timings, and/or change your CPU/memory ratio so that your memoryÂ’s FSB is always at/below itÂ’s rated speed. This should insure that your memory wonÂ’t be limiting your FSB, just your mobo.

Hopefully someone can make more sense of this than i did.
Nick

 

[Disillusion]

You would change the CPU to RAM ratio only if you have RAM that doesn't overclock well. Lets say for instance that your CPU can take 300 MHz, but the RAM can only take something like 250 MHz. When you raise the FSB (HTT with an AMD) it will automatically raise it for the RAM as well, so you must set up a ratio if the RAM is maxing out and your CPU isn't. For instance, if you set up a 5:1 ratio, if you increase the FSB from 250 MHz to 255 MHz, the RAM is only going to get 1 MHz more instead of 5 more.

The only way to find out the max FSB your motherboard can support is if your CPU can be overclocked (and is stable) further than the motherboard can go. Other than that, there is no way to find out the max FSB the motherboard can do.

 

[idiotec]

RAM is linked to the FSB, so raising the FSB also increases the speed of the RAM. All that is saying is to increase the RAM divider so you have headroom on raising the FSB before the RAM starts running at speeds higher than it is designed to.

The other thing you would want to do to test your max FSB is lower the CPU multi as low as it can go and make sure to lower the LDT multi as well.

One example, lets say you chip runs at 2Ghz and your running DDR400, default settings are:
CPU multi x10
FSB 200
RAM 200
LDT x5

Now lets say you do the following:
Lower CPU multi to x6
RAM divider to 2:1 (may look like 100Mhz in BIOS)
Lower LDT to x3

Now you can raise the FSB to 333 without the CPU, RAM or LDT being overclocked, get it? The results would be:

CPU = 6x333 = ~2Ghz
RAM = 333/2 = 166
LDT = 3x333 = ~1000Mhz

The main point is when trying to find one components max speed, you want to take other components out of the equation.

 

[Disillusion]

Ah, yes, idiotec. I forgot about dropping the multiplier down. I guess that would be a good way to find max FSB.

 

[NickFas]

What is the LDT?

 

[Twizted_3kgt]

LDT = hypertransport...you want to try to keep this around 1000mhz...fsb (or HTT) x LDT = hypertransport Mhz