Overclocking with Intel 975XBX motherboard

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I want to build myself a games computer for flight-sim (and other games) and
want to use the Intel 975 board (BOXD975XBXLKR) which can handle 2 PCI-e
video cards in SLI mode. Also want to use the Core2Duo E6600 CPU. While I
don't want to overclock initially I want the capability so I can overclock
at a later date if I find I require the extra grunt.

A couple of questions: are there reasons not to use that Intel board and CPU
combo (maybe other boards and CPU's are more suitable for overclocking)?
What size of powersupply do I need to drive the system with 2 video cards
and 2 hard disks, and I assume overclocking requires extra power.? What
performance gains can be achieved by overclocking a E6600 CPU?

Re: Overclocking with Intel 975XBX motherboard

oscar wrote:
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For Conroe, you want revision 3.04 or later of BadAxe. Earlier revisions
would not be a good choice for Conroe/Allendale. I think BadAxe is a
Crossfire board (ATI video cards) and not SLI (Nvidia video cards) ?

Badaxe users seem to use clockgen or equivalent type tools, to do their
overclocking. Presumably that is to bypass BIOS limits. (Clockgen is
used on other boards, so that a low clock is selected in the BIOS, to
get a good "strap" value [a parameter hidden from users], then Clockgen
is used to set the clock to a useful value, once in Windows. In that regard,
you still can make good use of Clockgen type tools, when overclocking
other Conroe/Allendale boards with Intel chipsets.)




Some other boards compared here:


( The latest thing is RD600, coming soon, maybe:

   http://www.hardinfo.com/show.asp?page=6687 )

So with some fat, two slot Crossfire cards, and a busted audio
implementation (EAX), one PCI slot is covered by a video card, the other
PCI slot ends up with your games-ready audio card. Leaving no PCI slots
for anything else on your BadAxe. Having the extra PCI Express slot is
sweet though, as a day will come when something useful will plug in
there (physics triple play?).

(Two double-slot ATI Crossfire video cards leaves a pretty crowded system...)
(Exhausting the video card heat out the back of the case, is smart.)

The power issue is quite variable. Conroes are decent lower power processors,
and if you start with a single modest video card, you could probably
get away with a 24 pin 350W power supply. The other extreme, is when using
two 120W ATI top end cards. Then you need 12V @ 20A for the video cards.
And now you are looking at a higher end power supply.

The problem is, the power on a board comes from different rails, depending
on the type of (high end) power supply used. Ordinary 24 pin supplies are
dual rail types. But triple and quad supplies also exist, up to the $400 to
$500 level. The load itself does not change, but which rail they load up,
changes with the power supply type.

E6600 is 65W. At 90% Vcore efficiency, that would be a 12V2 of (65W/12V)/0.90 =
You are unlikely to overload the CPU power rail of the power supply,
even when overclocked.

Video card power is split. On a 10 amp video card, 4 amps is via the
PCI Express slot contacts, and 6 amps is via the PCI Express 2x3 power
connector. For SLI, that is 2*4=8A on the main motherboard power
connector 12V rail and 2x6=12A via whatever rail drives PCI Express power
connectors. (I cannot get too specific here, as there are dual, triple,
and quad rail power supplies.)

CDROM = 1.5A on 12V. Idling disk drive = 0.5A or 0.6A on +12V. Allocate
0.5A for system fans on fan headers.

If we used a simple dual rail supply, the math works out this way, with two
high end ATI cards.

12V2 = CPU = 6A
12V1 = everything else = 8A + 12A + 1.5A + 0.6A + 0.5A = 22.6A

That is too much for most run of the mill dual rail supplies. (Dual rail
supplies stop at about 12V @ 20A per rail. The CPU rail is underutilized
and the dual rail supply capacity is being wasted on the CPU rail.)

One of these could do it, as the supply features a single 12V @ 34A
rail, which is enough for the 28.6A total load. The Silencer model
may run a bit quieter and can also do the job. Note that with
single rail output, there is no need to figure out which rail
a load ends up on.


I can also rummage around this list of power supplies, and see if
anything here might match the load. Even though this list is on the
Nvidia SLI enthusiast page, they are still power supplies that can be
used for SLI or for Crossfire.


This is an example quad supply. 18A on each of 12V1, 12V2, 12V3, 12V4.

Now, the first problem, is which load is connected to which rail.
Seasonic does not provide a wiring diagram for their quad rail supply.
(Neither does anyone else for that matter.) One possibility, is the
processor power connector, has both 12V1 and 12V2 for processor power
(suitable for a dual socket motherboard). 12V3 might be reserved for
PCI Express power. 12V4 for general motherboard and disk drive use.
Sometimes you can get definitive information from a web review of
the power supply (and a lot of research is needed then, when shopping).

Breaking down the sample numbers used above.

12V1 - No load (since the motherboard is not dual socket)
12V2 - 6A from the E6600 processor load
12V3 - 2*6A for the PCI Express 2x3 component of two video card loads.
        12A is less than the 18A max. (I'm assuming the two 2x3
        PCI Express video connectors are the only load on 12V3.)
12V4 - 2*4A for the PCI Express slot power pins, for two video cards.
        1.5A + 0.6A + 0.5A for minimal drives and fans. Total 10.6A.
        Again, less than the 18A max. (I'm assuming all motherboard
        loads, including the PCI Express slot power pins, fan headers,
        and disk drive power, is on 12V4.)

The unit passes. But of course, it can only pass, if we can get our
hands on a wiring diagram to verify these assumptions. The wiring
could be very different than this.

Single rail supplies and dual rail supplies offer no surprises.
Single rail (monster) supplies simplify life, as a wiring diagram
is not needed. Dual rail supplies place the processor on 12V2,
the rest on 12V1. The practical current limit of a dual rail,
limits their usefulness in high end systems. Triple supplies
can have 12V1/12V2 for dual socket motherboards, and 12V3 offers
more than 20A and powers everything else (sort of a "super"
dual rail in a sense). Quad supplies are a headache, as we
don't know for certain where the rails go. While 12V1/12V2 may
be for a dual socket motherboard CPUs, 12V3 and 12V4 have to be split
somehow, between all the rest of the loads. To be absolutely
certain, a wiring diagram helps, as you do want to do the bookkeeping

Supplies also have power limits on groups of windings. So
more than one limit can apply when doing the math. Four windings
may have an 18A limit each, but the total amps drawn simultaneously
from the four of them may be limited to 52A. Some of these group
limits are thermal in nature, or perhaps a common primary winding
is being used. But all the limits must be inspected as part of
the bookkeeping. We certainly aren't getting near the 52A
combined limit with this system, as the combined load is only

I suppose if you have the money to blow on a couple high end
Crossfire cards, picking up a $200 power supply isn't going
to kill you.

A posting the other day, said "flight sim is CPU limited".
Other games, like Oblivion Elder Scrolls, is GPU limited
even with dual video cards (Anandtech mentions this quite
frequently). You have to understand your gaming habits pretty
well (including what size and res of monitor you will be using),
not to make an expensive mistake buying hardware for it.

As a final treat, why are the pins on this guy's PCI sound
card burned ? The pictures at the bottom of the page, are
the result of plugging the Creative X-Fi into a BadAxe ???


Have fun,

Re: Overclocking with Intel 975XBX motherboard

Thanks Paul, for your detailed explanation. I'm overwhelmed! Didn't think
there was so much to consider. I have built (assembled) a few machines
myself, but never overclocked anything before. For this upcoming machine I
want the 'ability' to overclock if need be, so I want to choose the right
components, but to start I will run it at standard speeds, maybe just with 1
video card and see how it performs, and try to overclock later. Was thinking
C2D 6600, Intel 975XBX, 2GB RAM and a single Nvidia 7950GT video card.

My main interest is flight simulation, in specific the recently released FSX
which seems to need a high performance machine. Have to do ask some
questions in the flightsim newsgroup if Crossfire or SLI is a better
solution for MS Flightsim.

A few more comments (questions) follow below:

Does that mean any board that uses the 975 chipset is designed to use ATI
crossfire cards, instead of Nvidia SLI cards? Is there any other board that
might be more suitable for my needs, one that can use Nvidia SLI cards as
well as Crossfire cards, maybe a board with a different chipset?

Your detailed explanation of powersupply considerations is a surprise too,
thought any 500-600W unit from a reputable supplier will do. Well, think

 my thanks for your detailed reply - gives me a bit to think about.

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Re: Overclocking with Intel 975XBX motherboard


I'm running a C2D 6600 @ 3.24 ghz 24/7 stable and it's awesome!!!
make sure you get some decent memory, PC6400 from gskill, OCZ,
Corsair, etc.

If you're going to overclock, cooling is important.
For air, a Thermaltake Big Typhoon works well.
Replace the stock fan with a silverstone 110 cfm fan and you're good
to go.
You also might want to look into liquid cooling.
A GOOD 600 - 700W PSU will be necessary.
Coolmax and OCZ gamestreams are good names.

The 975X chipset does not support SLI per se. It does support
You can run Nvidia gpu's in sli with modded drivers on the 975X
chipset. Check Overclock.net for a link or write back and I'll get a
copy to you.

I would strongly recommend you consider the Asus P5W DH Deluxe for
your motherboard.
It is far better for overclocking!!!
I am very happy with mine as well as other Asus products.



Big typhoon:


Finally, performance gains are substantial!!

See www.overclock.net for anything you need to know.

Good luck,


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Re: Overclocking with Intel 975XBX motherboard

Thanks Al, for your reply. Glad to hear that your C2D 6600 overclocks so
well. Running that CPU at 3.2Ghz suggests a 30% performance gain based on
the increase from the standard 2.4Ghz. Are you using the Asus P5W DH board
and why is it better for overclocking? Are there overclocking utilities
shipped with the ASUS board, or must they be obtained separately. I assume
'overclocking' is all done with software, I guess the days of setting
jumpers are gone. BTW, what graphics card do you use, ATI or Nvidia?

Rgds, Oscar

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Re: Overclocking with Intel 975XBX motherboard


Overclocking is traditionally done in bios.
There are software overclocking programs such as clockgen, but these
result in overclocks that are often less stable.

Asus boards are traditionally overclock friendly in the sense that you
have a lot of control in the form of bios parameters which relate to
FSB, CPU voltage, memory voltage, north and south bridge chipset
voltage, etc.

Check out:

This us a newly released board employing the Nvidia 680i chipset (i is
for intel).

Nvidia chipsets have traditionally not been good for overclocking but
supposedly this has been resolved with the 680 series.

I currently am running an XFX 7900 GT which is overclocked to
550/1800. While the P5W DH Deluxe supports crossfire, you can run sli
with modded nvidia drivers.

I also enjoy flight simulator (fs9) and with my current setup, I can
run with all settings maxed and my framerates range from 30-100 fps
depending on the situation.

I have some spare cash right now and am purchasing a new 8800 GTX
today. I"m sure it's overkill for fs9 which is cpu intensive anyway,
but it's new and out there so what the heck??

Flight simulator will run on one core only. If you want to utilize
both cores, check out the following:


It helps a little with FPS.

I STRONGLY suggest you visit www.overclock.net and sign up. It's free.

There is a wealth of info on getting started with OC'ing. One warning,
it can be addicting!!!!

All the best,


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Re: Overclocking with Intel 975XBX motherboard

You may also find this helpful:
http://www.tomshardware.com/2006/10/11/four_975x_motherboards_for_core_2_duo /

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