Originally Posted by tomb18
GTL (Gunning Transceiver Logic) is a reduced swing I/O driver technology support high speed buses and backplanes. Typically it uses a reference voltage derived from the vrm's to establish the swing from 0.4V to 1.2V. If the reference voltage is increased the swing increases and the noise susceptability of the bus decreases.
The reference voltage is input directly to the cpu and is derived from the Vtt voltage on the vrm's. The intel specs say it is derived from precision 1% resister divider networks but it could also be done other ways as is the case in the rd600 board design.
There are no pull up or down resisters involved in this circuit (they on on the die itself) so it is unlikely a pencil mod will do anything. On the other hand if a board does use resisters to establish the reference voltage, then maybe it would work.
This voltage is really critical to the operation of the fsb and it is probably best to just buy a board that supports changing it in software.
But, perhaps all boards do but they just havn't made the setting of it accessible in the bios.
in short- if you dont have a GTLv adjustment, then adding FSBv WILL help stabilize, especially in the case of a Q4..as DualCores, do not require as much GTLv to remain stable at higher FSB's.
PLLv is related to the PLL clock and its value. Raising PCI-E freq typically requires that you raise the PLLv to prevent sata errors. In addition to the PCI-E clock, the PLL also controls the PCI clock.
..sorry for the 'brief' explanation on my previous post.
link for more topics on Q4 GTLv control and its affects on stability-> Here