Extreme overclocking / I
Motherboard requirements
Hirdetés
Overclocking Intel CPUs became somewhat difficult when Intel introduced the locked multiplier scheme for its processors. Difficult, but not impossible, as the final CPU speed is always multiplier x FSB and FSB is set by the mainboard and not the CPU. The CPU does tell the mainboard what FSB it is supposed to run on, but motherboard manufacturers have the choice of adding additional adjustable FSB speeds and usually they do. The story is exactly the same with the Pentium 4 - the multiplier is fixed, but mainboards have the chance of offering higher FSB speeds than 100MHz, which allows us to overclock our shiny new P4 to crazy limits... does it? Not exactly, as the P4 systems introduced a few new overclocking "factors". The system bus is quite happy at even 133MHz, that's no problem. RDRAM, however, feels quite ill at anything beyond a 10-15% increase. So, at a 120MHz FSB, you will surely get lockups not because of the CPU, not because of the GMCH failing, but because of RDRAM not being able to tolerate the 8 x 120MHz = 960MHz frequency. The CPU could also be a limiting factor, the point here is that RDRAM will always max out at about 110-115MHz, regardless of the CPU.
Luckily, there is a way to get around this, as PC800 RDRAM is not the only choice for P4 users. PC600 RDRAM is also available and all mainboards should be able to cope with them. All they do is that they adjust the multiplier of the RDRAM according to the information given to the board by the memory module. PC800 RDRAM uses a 4X multiplier, whereas PC600 needs 3X and since RDRAM multiplier is not locked, any mainboard capable of overriding the specified value and allowing the user to select between 4X and 3X has a huge "+" on the overclocking features list. Let's suppose we select a 133MHz FSB. This is something PC800 RDRAM definitely cannot handle, as 4 x 2 x 133MHz = 1066MHz is way out of range. On the other hand, if we set the RDRAM multiplier to 3X as if we had PC600 RDRAM, we would get 3 x 2 x 133MHz = 800MHz, which is exactly the spec for PC800 RDRAM. Adding the additional 10% tolerance most RDRAM modules have, FSBs of 145-150MHz are achievable this way! Let's sum up our findings. Every P4 mainboard expected to overclock well should have the general overclocking features:
- Wide range of FSB speeds, possibly with 1MHz increments,
- CPU Core Voltage (VCore) adjustments, at least up to +0.1V,
- Possibly RDRAM voltage adjustments (similar to I/O Voltage, or VIO, for short).
This would allow us to reach 110-115MHz FSBs if the CPU and RDRAM is right, for sure. If we wanted a true overclockers board, there is one additional feature that HAS to be there to unleash FSBs between 115MHz and 150MHz:
- Manual selection of RDRAM multiplier between 3X and 4X!
Currently, there are two mainboards that support all of these features: the ASUS P4T and the newly released MSI 850 Pro2. The first is the one and only ATX P4 solution from ASUS, it is based on a 6 layer design, doesn't come cheap, but has been the all-time favourite for P4 users due to its capabilities. The latter, MSI's newcomer is supposed to change all this, as it bears every feature of the P4T, but comes with a reworked 4 layer design and noticably cheaper. Both boards support Socket-423 (Willamette) P4 CPUs, up to 2.0GHz and if you seek to seriously overclock your P4 processor, you currently have no other choice than these two offerings. Not all Pentium 4 mainboards are created equal, remember?
A cikk még nem ért véget, kérlek, lapozz!
