X2 Bug Warning: Thermal throttling bug / power saving mode use could fry your CPU!

There's a bug in the current revisions of X2 CPUs wherein either
the thermal safety throttling may be unexpectedly forced off, or wherein
its use could cause the CPU core voltage to spike, possibly frying the CPU.

If the thermal throttling is forced off e.g. in the BIOS as is suggested
as a "work-around" for this bug, it's possible that some BIOSs would permit
the CPU to continue to run continually even if it has reached temperatures
beyond which the CPU could be damaged; normally thermal
STPCLK speed throttling would reduce the CPU clock to prevent this
damage from being so likely.

If thermal throttling is NOT disabled as AMD suggests the BIOS does, *OR*
if user selected ACPI ower saving / utility functions triggers STPCLK
mode while the CPU clock is running at normal speeds, the voltage spikes
caused by the instantaneous 100 Watt <--> 0 Watt Vcore load change could
cause the system to spike or undervolt Vcore leading to either a crash
or very possibly a fried CPU!

Everyone should confirm with their BIOS vendor and settings for their
ACPI / thermal monitoring options in the BIOS that they're running the core
at safe temperatures and in a way that will not trigger STPCLK throttling /
power saving!

Here's the info from AMD:

http://www.amd.com/us-en/assets/cont...docs/25759.pdf
Revision Guide for AMD Athlon™ 64 and AMD Opteron™ Processors 25759 3.51 06/16/05

124 STPCLK Throttling Causes Violation of VDD_ac Specification
on Some Dual-Core Processors

Description
STPCLK throttling during maximum power consumption operation generates large load steps and voltage transients that can violate the transient
voltage specification (VDD_ac). This problem is exposed on 4-layer
motherboards with single power and ground planes when the
core frequency is >2000 MHz.

Potential Effect on System
Violation of the VDD_ac specification leading to unpredictable operation.

Suggested Workaround
Do not enable STPCLK throttling on affected dual-core processors above 2000 MHz.

Fix Planned: Yes

Woah big potential bug that is!

While theyre at it, they might as well allow 1T timings for 4 X 512 sticks of ram in the memory controller.

=/ guess it's not time to hop on yet

wonder if this could be related to p4 dualcores cooking mobos due to power transients when going into thermal protection modes (its the motherboards at fault really since power transients are caused by the vcore vregs not being able to cope with the power requirements of the CPU).

Besides, if going from full load to all stop is that dangerous, then so is going from all stop to full load.

Also effects single core A64 "DH-E6" too.

well this is just great

Quote:

---

Originally Posted by NickK

Also effects single core A64 "DH-E6" too.

---

No, it affects dual cores, both Toledo/Opteron (JH-E6) and Manchester (BH-E6), at 2.2GHz and higher.

No single cores.

See page 11.

But this is not likely to be triggered by any power saving stuff, as the problem only happens when going from FULL LOAD to STPCLK.

And there's no mention of "frying your CPU".

Looks like amd is going the way of intel :). i'm sure their genius engineers will fix this in no time. i fully trust amd :).

:spill: ... :wasntme:

'Also effects single core A64 "DH-E6" too.' -- It effects
BH-E4 (only X2's)
and JH-E6 (X2's and Dual Core Opterons).

"wonder if this could be related to p4 dualcores cooking mobos due to power transients when going into thermal protection modes (its the motherboards at fault really since power transients are caused by the vcore vregs not being able to cope with the power requirements of the CPU).
Besides, if going from full load to all stop is that dangerous, then so is going from all stop to full load." --

I agree, it seems likely.
Personally I am very disappointed at the penny-pinching,
quality-corner-cutting philosophy of consumer electronics design including
motherboards. As a PCB designer I've always been inclined to select
PCBs with full ground plane & power planes for each major voltage when
designing boards a lot simpler and lower speed than 2GHz + PC motherboards!
It really boggles my mind that they'd have such a push to try to get PCBs
down to 4 layers for Socket 939 motherboards with PCI, AGP, DDR,
etc. etc. that's all quite high speed and high pin count.
I very much suspect that it's more of a matter of *luck* than *engineering*
that they work as well as they do. Even though STPCLK / STPGNT type
power throttling is an easy to generate extreme test case of power load
fluctuation from ~ Zero power to full load, I suspect that many software
situations involving CPU / I/O bursts do about as much variation of loading
on the time scale of nanoseconds to microseconds. If the EMI design and
power filtering, regulation, capacitors, PSU, etc. isn't up to the task of
providing clean transitions from STPCLK to Full Run I suspect it's not REALLY
stable running common software programs under stress / bursty conditions
either, and that's probably a major reason for things crashing / flaking /
burning out on many systems.

What's needed is just better quality motherboards, 6+ layer PCBs, more
conservative design margins of capacitors / power regulators, thicker PCB
power traces, etc.

Agreed. Completely and whole-heartedly agreed.

Great example are the Neo2 Platinums.. even at only 2600mhz and 1.63v on my winchester the neo2 platinum's mosfets sound like miniature MIG welders... although they dont get too hot at least.

This is partly AMD's fault maybe for not testing the CPU on every motherboard under the sun that it may run on, but it shows who cuts corners to produce their board cheap too, and who builds a more quality product to stand up to abuse.

I'm still trying to figure out all the common cases when this could happen.

I think from what I've read that

(a) STPCLK# can be set in chipset hardware semi-automatically
(e.g. via CPU overheat detection & then resultant clock-throttling to protect
the CPU's temperature but allow continued operation at a stuttered percentage
of normal clock operating time).

(b) STPCLK# signal is set by the chipset and can also be set via software
by causing certain chipset registers to be used to enter the STPCLK state.

(c) I think STPCLK# is the "hardware signal" (which can be set also by
software) that causes the STPGNT state in the CPU as an effect of its presence. I think STPGNT is what the CPU does when it sees STPCLK# active. This is a little confusing since these seem to get referred to as
if they're quasi-independent in some cases but often times there seems to
be a causal link implied.

(d) I've often seen it said that ACPI power state (C2) is what's effectively
in operation when the AMD CPU is in STPCLK# STPGNT state. I think
that's the usual case anyway from what I've read. I think the ACPI BIOS
writers might be at liberty to define what C1, C2, C3, S1, S2 etc. actually
do as long as they follow the overall rules of ACPI but I guess C2 is commonly
chosen to be the "STPCLK, STPGNT" mode.

(e) I've further seen it said that (S1) ACPI state is, for example, commonly
implemented using the STPCLK / STPGNT mode which would really mean
that in this case (S1) causes (C2) mode which is set up to work via STPCLK.
e.g. ACPI specification 3.0: pp 414:

"15.1.1.1 Example 1: S1 Sleeping State Implementation
This example references an IA processor that supports the stop grant state through the assertion of the
STPCLK# signal. When SLP_TYPx is programmed to the S1 value (the OEM chooses a value, which is
then placed in the \_S1 object) and the SLP_ENx bit is subsequently set, the hardware can implement an S1
state by asserting the STPCLK# signal to the processor, causing it to enter the stop grant state.
In this case, the system clocks (PCI and CPU) are still running. Any enabled wake event causes the
hardware to de-assert the STPCLK# signal to the processor whereby OSPM must first invalidate the CPU
caches and then transition back into the working state."


Given these findings it seems quite possible that, depending on the
BIOS involved, one could enter this problematic STPCLK# state from
"full speed" (>= 2000 MHz CPU clock) mode based on:

(a) BIOS / chipset / utility software thermal monitoring detection of
overheating on the CPU or other component.

(b) Any kind of power management / ACPI / APM type BIOS function or utility
that causes STPCLK# which might include (C2) or (S1) states depending
on your utility / BIOS settings.

I'm just not sure about "Cool N Quiet" I know there are tables of
power / clock / VCore settings and transition timings that it uses to
work. It's possible that some of those might use STPCLK to work; if
so I'd guess it'd be the ones that operate the CPU at "almost full speed"
but still reduced speed by some percentage like 88% or 75% of full speed.
At least on Intel chips this kind of clock dividing does indeed use
STPCLK to "burst" the clock between full speed and totally off in a given
duty cycle to achieve an average effective percentage throttling.
If AMD64 X2 CnQ uses this too then it's seemingly a risk for this
bug also.

What Socket 939 motherboards have the most robustly designed
Vcore power regulators with the most number of "phases"?

I've heard about 3-phase, 4-phase, 5-phase, etc. power converters
for Vcore generation but I don't know what common motherboards
for X2 / FX-53 / FX-55 Socket 939 really have the best regulator capacity.
Anyone know? How about for S-939 AGP boards?

AGP boards -- Asus A8V deluxe vs. MSI Neo2 plat vs. NVidia NF3 Ultra D?


Every time I see a reference to someone "over-volting" something to
"increase overclock stability" I sort of grimace and laugh. As an EE I know
that "too many volts" usually just fries ICs, and doesn't really help them
work "better/faster" in most ways. I think the MAIN effect of
"increasing the volts" to demonstrably increase platform stability is really
just to provide greater CHARGE / ENERGY into the "too-small" power filter
capacitors so that when there's a large fast-rising load like a high MHz burst
of I/O or computation that there's a better chance there'll be enough energy
in the little filter capacitors to sustain at least the minimally necessary
current / voltage to keep the electronics working correctly until the relatively
slow (in comparison) voltage regulators can squirt out more energy / current
to recharge the voltage on the filter capacitors up to the proper level again.

Thus what's really needed isn't MORE voltage, it's BIGGER / BETTER / MORE
capacitors and voltage regulators to provide more current / energy more
frequently to the CPU / chips when those burts of power are needed. If
this was done one should be able to run at 100% nominal Vcore / Vdimm / etc
and have as much of a overclock with no risk of overclocking causing
transient undervolting as is possible limited by the actual speed of the ICs.

More Vcore regulator phases with higher quality and amperage FETs per
phase should help this.

Evidentally this kind of STPCLK transient causing power regulator
instabliliy has been true for some time:
http://unixmafia.port5.com/news/00211001.html

"Overheating problems on some KT133(A) Motherboards, namely Asus
Last update: 2002-12-05
...The problem
The BIOS on several via KT133 and KT133A motherboards disable the HLT , STPCLK and STPGNT instructions of the processor (apparantly, some A7M266 boards have it too). These states are responsable for power savings (and heat production) under the APM and ACPI specifications. The boards that have these disabled therefor do not completely implement those specifications, although they do claim so in their propaganda.
This can have several reasons, but one of the most common is to hide the fact that a particular board has an inferior power-supply. Which seems to be the case with my Asus.
Asus uses a 2-phase power supply with 4 capacitators onboard, while most boards have a 3-phase supply with 6 capacitators. Especially the STPCLK instruction, which calls the C2 Power Management state of the Athlon processor, puts a heavy burden on the power supply, because switching between the lowest and highest power consumption can occur several times a second. The disadvantage of the C2 state is that it can interfere in realtime applications like video and audio, because it takes the processor a fraction of time to come out of it. Asus hides behind 'choppy audio' as a reason to disable both C1 and C2. If this were valid, why not supply a BIOS option to turn it on or off? "

For the Duron, but probably similar to Athlon X2 illustrating
some various ways STPCLK# / STPGNT is used and could be
entered from or exited to full-CPU-clock states --

http://www.asus-a7v.co.uk/A7V_Articles/KT133_Reg52.html

"...The STOP GRANT STATE (SGS) does pretty much the same thing, but it's a whole new animal when it comes to complexity.

From the Duron datasheets (with English comments in square brackets ;)

The AMD Duron Processor Model 3 enters the Stop Grant state upon recognition of assertion of STPCLK# input. There are two mechanisms for asserting STPCLK# ? hardware and software. The Southbridge can force STPCLK# assertion for throttling to protect the processor from exceeding its maximum case temperature. This is accomplished by asserting the THERM# input to the Southbridge. Throttling asserts STPCLK# for a percentage of a predefined throttling period: STPCLK# is repetitively asserted and deasserted until the THERM# pin is deasserted.

[1. The CPU can be placed in SGS by hardware. It's often useful for stopping the CPU when it gets too hot.]

Software can force the processor into the Stop Grant state by accessing ACPI-defined registers typically located in the Southbridge. Software places the processor in C2 by reading the PLVL_2 register in the Southbridge. In C2, probes are allowed, as shown in Figure 3 on page 9.

[2. Programs like MBM5 can also stop the CPU when overheating, but through software.]

If an ACPI Thermal Zone is defined for the processor, the OS can initiate throttling with STPCLK# using the ACPI defined P_CNT register in the Southbridge. The processor enters the Probe state to service cache snoops initiated by the Northbridge during Stop Grant for C2 or throttling.

[3. The CPU can be made to wait for a bit to finish off what it's doing before actually stopping.]

The Stop Grant state is also entered for the S1 system sleep state based on a write to the SLP_TYP field in the ACPI-defined power management 1 control register. During the S1 sleep state, system software ensures no bus master or probe activity occurs.

[4. This may come as a surprise, but you can also go into SGS when in sleep mode ;)]

After recognizing the assertion of STPCLK#, the AMD Duron Processor Model 3 completes all pending and in-progress bus cycles and acknowledges the STPCLK# assertion by issuing a Stop Grant special bus cycle to the AMD system bus. After the Northbridge disconnects the AMD system bus in response to the Stop Grant special bus cycle, the processor enters a low-power state dictated by the CLK_Ctl register. During the Stop Grant states, the processor latches INIT#, INTR (if interrupts are enabled), NMI, and SMI#, if they are asserted.

[5. When the CPU is told to go into the stop grant state, it'll finish off everything that's waiting to be done, and let the motherboard hardware know that it's going to stop. When the motherboard responds by halting normal communication with the CPU, the CPU goes into a low power state, ignoring everything apart from..]

The Stop Grant state is exited upon the deassertion of STPCLK# or the assertion of RESET#. When STPCLK# is deasserted, the processor will initiate a connection of the AMD System Bus if it is disconnected. After the processor enters the Working state, any pending interrupts are recognized and serviced and the processor resumes execution at the instruction boundary where STPCLK# was initially recognized.

[6. ...notification to wake up, or a system reset. When it wakes up, it starts communicating again, first doing any jobs that piled up whilst it was away, and then resuming normal operation]

If RESET# is sampled asserted during the Stop Grant state, the processor returns to the Working state and the reset process begins.

[7. If you reset your PC when it's in the stop grant state, it'll wake up and then reset as normal]


"...

You're overhyping this. Not that big of an issue, really, as long as you have adequate cooling.

Normal Cool'N'Quiet power-saving stuff will not trigger the problem.

Bug nest :rolleyes:

If it happens, you can RMA.

Quote:

---

Originally Posted by synergy

What Socket 939 motherboards have the most robustly designed
Vcore power regulators with the most number of "phases"?

I've heard about 3-phase, 4-phase, 5-phase, etc. power converters
for Vcore generation but I don't know what common motherboards
for X2 / FX-53 / FX-55 Socket 939 really have the best regulator capacity.
Anyone know? How about for S-939 AGP boards?

AGP boards -- Asus A8V deluxe vs. MSI Neo2 plat vs. NVidia NF3 Ultra D?


Every time I see a reference to someone "over-volting" something to
"increase overclock stability" I sort of grimace and laugh. As an EE I know
that "too many volts" usually just fries ICs, and doesn't really help them
work "better/faster" in most ways. I think the MAIN effect of
"increasing the volts" to demonstrably increase platform stability is really
just to provide greater CHARGE / ENERGY into the "too-small" power filter
capacitors so that when there's a large fast-rising load like a high MHz burst
of I/O or computation that there's a better chance there'll be enough energy
in the little filter capacitors to sustain at least the minimally necessary
current / voltage to keep the electronics working correctly until the relatively
slow (in comparison) voltage regulators can squirt out more energy / current
to recharge the voltage on the filter capacitors up to the proper level again.

Thus what's really needed isn't MORE voltage, it's BIGGER / BETTER / MORE
capacitors and voltage regulators to provide more current / energy more
frequently to the CPU / chips when those burts of power are needed. If
this was done one should be able to run at 100% nominal Vcore / Vdimm / etc
and have as much of a overclock with no risk of overclocking causing
transient undervolting as is possible limited by the actual speed of the ICs.

More Vcore regulator phases with higher quality and amperage FETs per
phase should help this.

Evidentally this kind of STPCLK transient causing power regulator
instabliliy has been true for some time:
http://unixmafia.port5.com/news/00211001.html

"Overheating problems on some KT133(A) Motherboards, namely Asus
Last update: 2002-12-05
...The problem
The BIOS on several via KT133 and KT133A motherboards disable the HLT , STPCLK and STPGNT instructions of the processor (apparantly, some A7M266 boards have it too). These states are responsable for power savings (and heat production) under the APM and ACPI specifications. The boards that have these disabled therefor do not completely implement those specifications, although they do claim so in their propaganda.
This can have several reasons, but one of the most common is to hide the fact that a particular board has an inferior power-supply. Which seems to be the case with my Asus.
Asus uses a 2-phase power supply with 4 capacitators onboard, while most boards have a 3-phase supply with 6 capacitators. Especially the STPCLK instruction, which calls the C2 Power Management state of the Athlon processor, puts a heavy burden on the power supply, because switching between the lowest and highest power consumption can occur several times a second. The disadvantage of the C2 state is that it can interfere in realtime applications like video and audio, because it takes the processor a fraction of time to come out of it. Asus hides behind 'choppy audio' as a reason to disable both C1 and C2. If this were valid, why not supply a BIOS option to turn it on or off? "

---

I suspect this is the way it is happening.

In theory adding more voltage until the described affect creates a highly logarithmic increase in need for voltage shows how much "power" your board is capable of handling.

For example:

A processor scales well with voltage on one board, but not as well with another.

This implies that the board is at fault, and if placing an X2 onto the weaker board you may pass the maximum the board can deliver at even default settings (assuming first tested CPU was a single core A64).

This problem isnt exactly new either. Older KT133/KT133a boards only supported up to a certain CPU due to the power draw higher models required. Even KT266/266A had this problem. Some which stopped at a certain point were just because the manufacturer was too lazy to update the BIOS microcode (board was fully capable of going beyond "max" suggested CPU) but many (Epox 8kta3+, Asus A7V133, MSI...) couldnt handle it, even some running recommended CPU's couldnt.


What i'm trying to point out is that this is not a new issue at all.. and its not being hyped at all if you remember past experiences.

EDIT

I should mention that I very much dislike temperature protection that is dependant on the BIOS.

If a small IC were used to monitor PWM/Choke/CPU temperatures (accurately) and connected to the power switch (or a secondary one) so it could power off the machine even if the CPU had failed and was locked up this would be a much better solution.

better yet if a temperature resistant co-processor were placed on the motherboard or CPU die that would function and maintain power loads (high power resistor may be required intermittantly) to reduce transients when the "master" processor(s) failed we wouldnt have this problem at all..


And why does asus always skimp on parts? If memory serves correctly they completely removed the vref circuitry from their GeForce 3 boards feeding 3.3v direct to the I/O of the memory chips (not VDDR which can be taken as high as 3.8v at times with voltage modifications)..

I think it's "underhyped" in that many motherboards have
very marginal quality / capacity design for their PCBs, voltage
regulators, and filters.

AMD designed the X2 so that it'd be compatible with the Socket 939
"design envelope" of heatsink and motherboard design so that it should
be supportable properly on all well designed motherboards and PSUs of
adequate capacity with only a BIOS change.

However the X2 *does* consume just a bit more power than ANY other
AMD Socket 939 CPU that has ever existed including the FX-53/FX-55 or whatever, and certainly uses a fair bit more power than a common
single core Athlon 64.

So as STEvil said, any motherboard that is "marginal" with respect to
stability / current / voltage regulation for ANY other AMD processor
even under overclocking conditions will perform even worse and more
marginally / unstably given the use of the even more power demanding X2.

The main issue that limits PCs stress test or overclock stability is probably
EMI (noise causing data corruption) and voltage / current limitations causing
glitches of the logic and undue stresses on the ICs and the integrity of the
electrical waveforms.

If one model of motherboard can consistently overclock a given CPU
to a higher frequency while using lower (e.g. stock / nominal) voltages than
another model of motherboard, the one that achieves the best overclock
at lowest voltages must have superior timing PCB layout and EMI / power
design.

This STPCLK issue is probably a decent "acid test" of a motherboard's Vcore
power supply regulator phases and PCB / capacitor layouts to keep the CPU
happy even under frequent and extreme load spikes in the case of working
when going from STPCLK mode to RUN mode. It wouldn't make a bad
"benchmark" type stress test, really, if someone actually made software to
check for corruption / glitches and to stimulate this "on off on off" behavior
many times a second.

Will it fry your CPU / motherboard? Well the CPU could get overvolted
if the Vcore regulators / traces "ring / spike too high" when the load
is suddenly shut off (STPCLK happens from full load).

It could also overvolt / ring too high when the CPU is stopped and all of
a sudden there's a huge load demand (STPCLK is removed starting running
again) and the regulator feeds the maximum possible voltage onto the CPU
to compensate for the detected undervolting due to greatly increased load.

At the least it's a high stress on the "pass current" and dynamic loading of
the MOSFETs, CAPs, and could cause these to fail quickly.

At the worst, it could glitch the CPU in a way that might fry it due to either
overvolting spikes or undervolting "reverse voltage" situation where VIO is
set to a normal level while Vcore is very much too low.

I agree with STEvil that the "over-temperature" protection design
isn't really something that is something that should normally occur
(since even overclocked X2s tend to run fairly cool), and that it's not
the best thing to rely on anyway. However if you DO have a fan
failure or over clock generation glitch or whatever that DOES cause the CPU
to run way too hot, you'll be in for a potentially nasty surprise
(possibly smoke, flames, melted solder, ruined CPU / motherboard) if
the "last resort" C2 / STPCLK thermal throttling does NOTHING because,
according to AMD's suggested workaround for the problem, the BIOS
just DISABLED the STPCLK mode!

And in a more common / serious situation, I am still unconvinced that:

(a) Cool N Quiet or other ACPI functions on BIOSs that *DON'T* disable
STPCLK mode cannot trigger this kind of crash inducing glitch if they're
trying to run the CPU at 90%, 80%, 75% or similar frequency since
in those cases one could still be at 2000, 2200 MHz clock and maybe using
STPCLK throttling to achieve the reduction.

(b) that other kinds of power saving states other than CnQ won't enter
C2 or other states that use STPCLK.

Furthermore even hypothesizing if STPCLK is disabled in BIOS,
even if CnQ can't cause this problem, any motherboard that'll fail
Vcore regulation BECAUSE of STPCLK issue is *STILL GUARANTEED*
to be unstable under stress testing of running normal software since
there is very likely *SOME* combination of software and I/O related
events that'll cause a similarly large variation in "low CPU activity to high
CPY activity" that'll cause too much of a Vcore current demand transition
and STILL crash / corrupt the PC. And THAT will be on a day-to-day
gaming / computing / overclocking basis what may cause system
crashing / flakiness.

Personally I want a motherboard that is well enough designed that
it CAN pass the STPCLK test at 2200+ MHz and not glitch!

In other words, hold on to your wallet till AMD fix this bug! :D :D :D

Quote:

---

Originally Posted by terrace215

No single cores.
See page 11.

---

Your quite right - perhaps reading the forums at 5:30am isn't such as good idea! :D

"In other words, hold on to your wallet till AMD fix this bug!"

Yes, but the best "fix" is for AMD to come out with their new
Socket and Chipset design to replace Socket 939 with one that'll
let the CPU have more current / power, more power supply pins, etc.

If we're just talking about Socket 939 and living with existing CPUs and chipsets,
the best "fix" would involve mostly better quality motherboard PCBs and
motherboard power regulators and only secondarily some CPU changes AMD could
make (capacitors under the heat spreader maybe?).

Otherwise I think what they are really admitting here is that the X2 is using
almost twice the power of common Athlon 64 CPUs, and even 10% more power than
the most hungry FX CPUs and that so many motherboard manufacturers
"penny pinched" and compromised so much on cost vs. quality that motherboards
that work well with Athlon 64 3200's may just be too poorly designed to
handle X2 CPUs under stressful / extreme circumstances.

I'd rather pay $50 more for a ROCK SOLID motherboard to put a high end CPU like
X2 into than to buy a ferrari of a CPU like the X2 and have to settle for putting it in
a second-rate motherboard! Problem is I'm not sure many or any Athlon64
motherboards are REALLY designed to handle this level of extreme computing
performance!

Current draw has always been the unspoken issue.

I was worried about it when I first read about the X2 - two cores will draw twice the core when overclocking too.. so each 100MHz increase is going to put more strain on the motherboard than a 100MHz clock of an FX57.

That's one issue.


The second issue is the removal of the safety mechanism - back to the t'bird days of ensuring that your CPU fan header shutdown check is running in the BIOS..

Quote:

---

In other words, hold on to your wallet till AMD fix this bug!

---

technically its not AMD's fault (and its not even a bug to be true).

its the motherboard manufacturer not designing up to spec


-edit3- I think it would be pertinant to examine boards spec'd to run dualcore p4's ;) /edit3


HOWEVER

Dont forget AMD said (paraphrased, etc) "any 939 board that will support an FX55 will support X2"..

Looking back to when that was said, it seems it was power regulation they were possibly hinting at.