Core i7 - Is High VDimm really a Problem?by Gary Key on October 8, 2008 12:00 PM EST
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Numerous articles and forum posts have been popping up recently about the potential of high VDimm settings damaging or destroying the upcoming i7 processor series. Will high VDimm cause damage? The answer to that question is not so simple actually. Unfortunately, due to the current NDA status, we cannot go into detail about this subject matter but can provide a general brief on it.
Our answer at this time is Yes and No. It sounds like we are straddling the fence but in actuality the correct answer depends on the available BIOS options, BIOS settings, memory selection, and final voltage settings. Intel’s stance is clear on this subject, run VDimm higher than their 1.50V~1.65V guidelines and you will affect the life span of the processor.
Exactly what the impact to the processor will be is dependent upon several factors. Put simply, if you go crazy with VDimm, let’s say around 2.0V~2.2V without additional tuning, then expect to greatly reduce the processor lifespan to a few weeks or maybe days. We have already witnessed several CPUs being damaged or destroyed at the motherboard partners with high VDimm settings, especially those that ran at 2.0V or higher with base settings. By base settings, we mean configuring an i7/X58 platform in the same manner a typical user now sets up a Penryn/X48 DDR3 platform. The rules have changed completely for Intel, just we cannot discuss the playbook at this time (hey, it is frustrating for us also).
Likewise, we have seen high VCore/VDimm test beds operate without a problem for benchmarking purposes (yet still fail with long-term bench testing) provided a multitude of BIOS settings for the core, DIMM, IMC, Uncore, and QPI selections were properly set. The base secret (there are more) is maintaining correct amplitude levels, something we will discuss at product launch. For now, high VDimm is not necessarily the true problem here, but it is the quickest way to damage/destroy an i7 if the rest of the system is not properly tuned.
However, we highly recommend keeping VDimm at or below Intel’s recommendations along with proper BIOS settings for the long-term health of the i7. Upcoming DDR3 products from the major memory suppliers will all support low voltage DDR3-1066~DDR3-1600 operation with fairly aggressive timings. This is key as the retail 920/940 processors will not be memory multiplier locked. In addition, the vast majority of JDEC spec DDR3 memory currently on the market will operate fine on the X58, albeit at slightly higher memory timings in some cases.
The extreme performance modules will also operate correctly, as we have found in testing to date, just at higher timings in order to meet the voltage guideline requirements. Certain performance modules that require 1.8V or higher upon POST will probably not work correctly (POST) unless the board manufacturer steps outside of Intel’s guidelines. In that case, you can replace the memory, reflash the SPD if the supplier allows, or toss in a pair of JDEC spec modules (current 1066 is fine), correctly set the voltages and timings that you require in the BIOS, shutdown, and reboot with the performance modules. Realize, this does place you outside of the guidelines but most users that fall in this category are already outside the lines anyway.
Personally, with the right board, cooling, and BIOS settings, 1.7V~1.8V should be fine (no promises yet) and will allow the upcoming low-voltage, high clock speed DDR3 DIMMS to reach the 1866~2200MHz level. This should satisfy most performance enthusiasts, but probably not the extreme clockers who will try for more. For the rest of us, this platform offers simply amazing bandwidth and latency numbers with tri-channel DDR3 1066 or DDR3 1333. In fact, we think tri-channel DDR3-1333 at 5-5-5-12 timings or DDR3-1500~DDR3-1600 6-6-5-15 settings (1.65V) will provide optimal memory bandwidth, write speeds, and latencies for 95% of the 920/940 users at this point. So, unlike the P45/X38/X48 platforms, having low-speed rated DDR3 is not going to be a hindrance to extracting fantastic performance from a i7/X58 setup.