Asus A7V333 Manual page 14

It gets more confusing with the ROMSIP jumper. The manual states: This jumper selects the source for data to set functional
parameters fir the CPU. The default setting [1-2], enables present ROM data access from the chip. Resetting the jumper to [2-3]
enables the use of BIOS to set CPU parameters. Phil Marlowe once said to me: Dead men don't wear plaid. That was 20 years ago
and I still have no clue what it means. We may have some more info on this matter shortly, so stay tuned.
DDR Voltages
When it comes to running voltages out of spec, hardly any manufacturer has the kind of track record as ASUS. From the P5A to the
A7M266, the road has literally been paved with burned DIMMs and the A7V333 threatens to continue this tradition.
The layout of the VDDR jumpers has been carried over from the A7V266-E, that is jumpers JP1 and JP2, only the values have
changed. By default, the A7V333 supplies a whopping 2.78-2.85 VDD and VDDQ (DDR core and I/O voltage). The variation
accounts for the differences in measurement on several boards. Changing the jumper configuration allows settings between 2.59 and
3.06V. The detailed settings are:
ii 2.59 - 2.63V (same with one or both jumpers removed completely)
i! 2.78 - 2.85V (default setting, out of spec according to JEDEC guidelines)
!i 2.88 - 2.96V
!! 2.95 - 3.06V
The latter two settings are almost guaranteed to destroy the memory modules, maybe not today but after a few weeks. It is not clear
what the purpose of the high voltage settings is, however, it is only a matter of time until this will become a liability issue for ASUS,
one way or another. Keep in mind that the settings are not documented and the high settings are not meant for "public consumption"
by ASUS either.
The interesting thing about these settings is that all current high-end DDR chips are using internal voltage regulators to reduce the
core voltage to 1.8V which is necessary to run at high frequency. The only parts of the chips that actually see the increased voltage
are input/ output buffers and, granted that those will wiggle a bit faster at higher voltages, the net effect is counteracted by the fact
that the internal voltage regulators produce a lot of heat that will overall slow down the chips. In other words, a sensitive approach
would be to leave VDD alone but increase VDDQ. Admittlely, there are some older DIMMs that will run at 2.5V internally but those
will hardly be used in PC2700 mode of operation which is the only scenario where the massive overvoltage would be of benefit.
The recommendation in this case is, similar as what we suggested for the A7M266: simply take off both JP1 and JP2 to bring the
voltages back to where they belong. Side effects are that the failure rate, that is, stuck bits and system crashes in memory-intensive
applications go down quite dramatically. In addition, we saw up to 3 % system performance increase in Expendable at the lower
voltage. It is not completely clear what causes this performance increase but any electronics will run faster and cleaner when they
run cooler.
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