E6750 Calculation Error @ 436 FSB

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I get a Code 4 Error from OCCT and a Rounding Error from Prime 95 almost
immediately after changing the FSB setting from 430 to 436.  I guess this is
telling me I'm at the limit of something.  I am using Corsair DDR-800 C4
memory set to 2.1v and 4-4-4-12 timings on a abit IP35Pro MB with a Zalman
cooler.  I have not changed any of the other voltages or settings in the
BIOS.  The system is stable at at the 430 FSB or 8 x 430=3.44 but I keep
reading about the E6750 running a 3.6 with no issues.  Is it the memory
timings?  If so, what is the trade off of faster cpu speed versus slower
memory timings?  I said I only want to do some minor overclocking but greed
is setting in!  Would faster DDR2-? memory make any difference?

Re: E6750 Calculation Error @ 436 FSB

'Ken' wrote:
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The most important bit of information you left out of your post.  What is
the CPU core voltage setting?
You did not post any of your temperatures; CPU core, motherboard, ambient...
'Zalman cooler' isn't a very precise description, as Zalman make more than
one model (and many of us have never seen a Zalman up close or installed.)

You haven't described the BIOS options you did not change.  Now we COULD
download the manual for your motherboard and look at the BIOS screens, but
can't you help us out?  Most of us don't have an aBit IP35 Pro motherboard.

Overclocking an Intel CPU is done by taking advantages of the design and
manufacturing practices Intel uses.  Intel puts out a CPU chip that has an
EXTREMELY good chance in working in marginal motherboard, high ambient
ambient temperatures, and with marginal power supplies and other substandard
components.  That keeps down the number of CPU returns and builds a good
brand reputation.  In addition, all CPU cores of the same series are made by
the same process on the same production lines.  The cores are tested and the
clock speed is then set at the factory, with the best performing cores set
with higher clock speeds.  As manufacturing a particular series of CPU cores
continues, quality control improves, with eventually nearly ALL the cores
meeting the highest clock speed standards.  At this point in the 'learning
curve' nearly all the cores in that series, no matter what the 'factory set'
clock speed, can be very easily overclocked to the maximum 'official top
factory speed'.  To overclock still more, then trade-offs must be made.

The are several trade-offs:

#1.  Keep the CPU core cooler than than maximum operating temperature
guaranteed by Intel.  (It also helps to keep ALL the other components cooler
than the maximum operating temperature.

#2.  IF necessary, raise the CPU core voltage by a VERY small percent.
[Check operation, if CPU stress tests show errors, raise the CPU core
voltage by a small increment, say  0.05 volt, check for errors.  Repeat
until you get error free operation... then you can try raising the clock
speed again.  BUT, do not, under ANY circumstances, raise the CPU core
voltage by more than 0.20 volts or so for a 45 nm Core 2 CPU.]  This helps
get higher clock speeds because as the core design approaches its limiting
speeds, the waveforms of the various pulses skew and have slower rise and
fall times.  The higher supply voltage results in higher pulse voltages and
helps the transistor switch faster, reducing the skew and speeding raise and
fall times.

#3.  A good power supply with adequate, well-regulated and well-filtered
power helps keep the CPU core voltage where you have set it.

#4.  Good quality support components help keep the signals going TO the CPU
within specifications so that the CPU which is operating OUT of
specification has fewer ill-shaped and/or ill-time signals to deal with.

THERE ARE NO GUARANTEES in overclocking a CPU.  Your particular, individual
CPU just may not allow the overclocking heights you may read of in websites.
Stuff happens.  Also, you can't absolutely  believe EVERYTHING on the web B^

Faster memory?  In your BIOS you can set the ratio between the CPU clock and
the memory clock.  If you have slower memory (which you do), then the ratio
can be set so that the memory will be running within spec no matter what you
CPU clock speed.  You have your FSB at 1720 MHz, quad-pumped, so the CPU
clock is 330 MHz.  You have DDR2-800 memory [NOT DDR-800 memory] so the
internal clock on the memory chips is doubled.  For this memory to run in
spec (DDR2-800 spec), the ratio between CPU clock and memory clock must be
set to 2:1 {430 MHz : 215 MHz, meaning your memory will be running at  215
MHz x 2 = 415 MHz} or 3:2 {430 MHz : 287 MHz, meaning you mayor will be
running at 287 MHz x 2 = 574 MHz, or 4:3, or 5:4.  At 1:1 your DDR2-800
memory would be running a slightly above spec, the equivalent of DDR2-860.
Now it may be that your memory CAN run slightly above spec.  Or it may be
that you memory is the reason you have problems at 436 MHz CPU clock (1744
MHz FSB) IF your CPU clock : memory clock ratio is set 1:1  (436 MHz x 2 =
DDR2-872 equivalent.)

The terminology for the CPU clock : memory clock ratio differs among
motherboard manufacturers and sometimes the numbers on either side of the :
are reversed.  Your manual may be ambiguous or worse, as if were written in
one language, translated to be proofed in a second translated to a third for
corrections, then re-retranslated for distribution.

Increasing the memory voltage can help operations at higher than specified
speeds.  Increasing the memory timings (4-4-4-12 to 5-5-5-15) can help.
BUT, the first thing to do is adjust the CPU clock : memory clock so that
your memory IS working at DDR2-800 or lower spec.  With your memory running
at less than its highest specified speed there will be a relatively small
performance loss of a few percent for most applications when little
multitasking is going on.

DDR2 memory is cheap now, so, IF YOU GOTTA BE GREEDY, then you could gain
more than 10% performance  by using higher rated memory.  Just keep in mind
that diminishing performance increases and increasing incremental costs will
eventual bring you to the point where you might as well be satisfied with a
30 to 50% overclock.

Fourteen months ago I built a system using an E4300 with DDR2-1066 (PC8500)
memory on an EVGA nVidia 680i motherboard (2 X 1 GByte modules totaled more
the $230 US).  I run the E4300 at a 50% overclock (2.7 GHz) with a CPU core
voltage 0.1 volts LOWER than specified.  The FSB is 1200 MHz (300 MHz CPU
clock) and the memory with a 600 MHz clock, so the DDR2-1066 memory is
somewhat overclocked at DDR2-1200 equivalent [keeping the same ratio
terminology {which is actually different than that used by my motherboard
manual}, the CPU clock : memory clock i8s 1:2]. I have a ThermalTake i7 air
cooler (a stack of about 20 thin square fins connected by heat pipes to the
CPU heat spreader.)  I can get as much as ~ 3.3 GHz, but to do so I must
increase the CPU core voltage by what I consider a dangerous amount.  Any
greater speed would require water cooling, further gains might be very
marginal.  I have two water cooling systems, but it just doesn't  seem worth
the trouble.  At this point I have a system that performs well for my
purposes, so I am anticipating keeping it as is when I built a 'Nehalem'
system next year (which will require a new CPU, motherboard, and  memory at
the least.

Keep in mind that Intel CPU's will lock up and cool down before catastrophic
heat damage (or any detectable damage) occurs.  On the other hand, raising
the CPU core voltage too much will instantly destroy the CPU.  Anything 10%
or more above the specified  voltage may be a step too far.

Finally, even if a CPU stress test throws an error at a certain clock speed
and temperature, you system at that speed may be completely useful for non
critical applications (games) or applications that won't generated nearly as
much heat, nor even use some of the CPU circuitry that the stress tests do.
And some stress tests (Orthos, for example) can be set to mainly stress the
CPU or to included more or fewer memory operations.  Some stress test can
generate more heat than any known real-world application (TAT, for example.)

Read, experiment (carefully), keep good records, have fun.

Good luck.

If I have made misstatements, I'm sure that one of the many knowledgeable
contributors to this Usenet newsgroup will offer corrections and clarify
what I've made obscure.

Phil Weldon

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Re: E6750 Calculation Error @ 436 FSB

Sorry for the missing 2 on the DDR.  Call it a typo!

The cpu voltage is set to auto in the BIOS.  OCCT says the voltage is at
1.18v when idle and 1.31v when running at 100% load.
The CPU Temp is 37C when idle and never gets above 59C under 100% load.
Core Temp, HWMonitor and OCCT all agree on the temps.
The room temp is 74F.
The maximium temp for this cpu is 72C according to a table from the Hardware
Secrets web site.
The system has a Zalman 9700 NT cooler -maybe not the best but itlooks nice
and works pretty well.
The MB control the fan speeds.  HWMonitor says the cpu fan is running at max
speed when the cpu is under load.
The system has a Corsair 620 HX power supply.  Supposed to be a very good
The memory is Corsiar Twin 2x2048-C6400 C4 or DDR2 800 and is rated at
4-4-4-12 when the voltage is set to 2.1v.
The abit IP35 Pro MB gets great reviews for quality and overclocking
capibility.  (I have built a new system ever year or so for the last 10
years and have always used ASUS MB's.  The abit MB is clearly better in my
humble opinion.  In fact, I went and bought a second one for my "backup"
system.  It has an "old" E6600 running at 9 x 346 or 3.1.  No problems yet
since I have not got up to the 400 DDR2 800 wall.)

Thanks for all the information.  I think I have decided to settle for 430 x
8 and be happy.  I don't want to get into playing with voltages, etc.  I was
just curious why both Prime 95 and OCCT failed immediately with a
calculation error when the FSB was increased beyond 430.  I know I'm pushing
the memory past its rated speed and I thought that is the error they would
report (memory) or just hang the system.

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