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[Anandtech] Intel X38 Tango - Getting down and dirty with VMCH

post #1 of 8
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Introduction
Quote:
Just about every review site has taken a unique approach to motherboard testing at one time or another, especially when it comes to overclocking. Over the last few months, we have taken a slightly different approach with the performance-oriented motherboards by offering additional technical information and a few BIOS guides to help end-users set up the ever more complicated BIOS functions that are available on today's boards. Our primary directive is to ensure everything we achieve in the cozy confines of the labs is fully repeatable with the same off-the-shelf retail components and settings.

The basic test criteria we use when overclocking the Intel enthusiast boards is setting FSB speeds in the 400-465FSB region. We ensure tRD is set as low as possible while keeping component voltages to a minimum level for stable long-term use. This type of overclocking might not sound very sexy - Patrick Swayze would dump us fast for not doing the Argentine tango with high FSB rates. However, our recent forays into dissecting DDR2 and DDR3-based motherboard overclocking have shown that tRD (Read Delay) is the most important tunable BIOS option available to the overclocker when seeking measureable performance improvements when overclocking Core 2 processors.

Those who wish to increase their insight or review just what the Northbridge strap setting and tRD are, how they both work, and why we are enamored with these settings are advised to read this article first and parse through this one for additional background information. Most overclockers are thoroughly aware that increasing processor voltage is required to allow speed scaling, but may fail to realize that raising MCH voltage is necessary when using a higher processor multiplier. The primary reason is to cope with the additional data throughput via the chipset busses as FSB levels rise.

Early implementations of the P965 chipset allowed FSB scaling to reach levels that were unheard of (in conjunction with the Core 2 Duo) by increasing the overall chipset latency at certain FSB points. Quite often, the deficit in chipset latencies at higher FSB speeds was enough to nullify a processor core speed increase of 100Mhz or more - meaning that a higher FSB overclock would trail the performance of a lower CPU speed using a lower FSB and higher CPU multiplier (due to Northbridge strap latency changes). It was not until the P965 was about to be replaced by the P35 that we finally began to see the release of high performance 965 boards - namely the Abit Quad GT and the DFI P965-S "Dark". These boards locked the 1066 Northbridge strap, while allowing Front Side Bus speeds near or above 500FSB that retained linear performance scaling to some degree.

To date, we have noticed that properly tuned Intel P35/X38/X48 chipsets also feature near linear performance scaling as FSB speeds rise. In fact, although NB strap changes are available manually, the straps really do nothing at this point but allow the use of different memory dividers. We are finding that increases in Northbridge voltages between a 6x and 7x multiplier may not be huge if even needed, but when we step over to the 8x multiplier (at equivalent settings) we have noticed a major jump is usually required in VMCH to hold the applied overclock "stable".

This is true even on the latest top-end motherboards featuring the X38/X48 chipsets. Therefore, using an 8X or 9X multiplier to show a high FSB holds more merit to the board and CPU capabilities than using a 6X multiplier to show off a board's high FSB capabilities. If a board can achieve a high stable FSB with a higher multiplier, it makes sense that a lower multiplier will have no problem achieving the same or greater FSB speeds.

For the seasoned overclocker nothing we have said above is anything new or groundbreaking. Our main goal though is to remain realistic for our readers, so that we show what is really possible rather than something that can only be held together with chewing gum and sticky tape for 5 minutes for that impressive SuperPi 1M screenshot.


Quick Thoughts
Quote:
As you can tell from the tone of this article, we care quite a bit about overall system performance, not to mention stability. Even if the gains are small, why not do things properly? What this little journey has proven to us is that the X38 (and X48 is similar) is clearly designed for optimum use at around 460FSB with higher multiplier processors.

For those who aspire to find the holy grail of 4GHz using a dual-core 45nm processor, we think the E8400 and a 9X multiplier is the sweet spot based on current test results. We will go into additional detail on the E8500 in an upcoming article that will feature "RDWI" - no, that is not a new driving while intoxicated offense, but detailed information about optimum tRD scaling windows.

In the end, we believe that a balanced and optimized platform is much more important than one that shows off high FSB speeds at the expense of performance, thermals, and stability. After all, would you rather have a balanced dance partner that can perform a variety of dances from ballet to hip-hop, or do you want someone that only looks good tap dancing after a few Red Bulls but quickly burns out?
post #2 of 8
tRD affects bandwidth on a 965 mobo in a huge way. I especially like this part.

Quote:
For the seasoned overclocker nothing we have said above is anything new or groundbreaking.


Great find, none the less.
*I use DFI Infinty Dark's for all of my client builds. They absolutely rock for a sub-100$ mobo with uber OC options.
post #3 of 8
No tests with a quad? BOOOOOOOOOO
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post #4 of 8
They dont need to do tests with Q4's... the test results show that the phenom is a characteristic of the mobo chipset ... not of the cpu. Hence, it doesnt matter what cpu they used to determine this, as long as they tested more than one cpu with different stock multi's.
post #5 of 8
Quote:
Originally Posted by CL3P20 View Post
They dont need to do tests with Q4's... the test results show that the phenom is a characteristic of the mobo chipset ... not of the cpu. Hence, it doesnt matter what cpu they used to determine this, as long as they tested more than one cpu with different stock multi's.
Well it depends if people would like to see stability tests on higher FSBs before buying the board, as it's hard to get quads stable at hgiher FSBs.......

BTW that's some INSANE bandwidth on those DDR3 modules......
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post #6 of 8
The only bad thing about the X48 is that it wont support DDR2
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post #7 of 8
I guess.. That seems like a different 'article' altogether though. You want stability with a Q4 at a high FSB.. get a good NB cooler and a mobo with an 8 phase circuit design.

I wish they would have shed some more light on the 965 rev differences between C1 and C2. Not many people realize the tremendous impact it has on OC potential and FSB scalability.
post #8 of 8
Quote:
Originally Posted by Akshay View Post
The only bad thing about the X48 is that it wont support DDR2
Actually the ASUS Rampage Formula supports DDR2........but I have no idea where to find one.
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