Two 6 pin PCI-E for HD 2900XT

[antonfrompresto]

I know that the HD 2900XT has a 6 pin and 8 pin PCI-E socket. From what I have read it seems to run fine with two 6 pin PCI-E but I am unsure of whether there are any issues associated with using two 6 pin PCI-E. Will a HD 2900XT overclock as much as with the official 6 pin and 8 pin setup or would I have to settle for a more mild overclock if I had to go for the two 6 pin setup?

Thanks, Anthony

[Lane-k]

many WR have been made with only 2x 6pin when the card was out.. with the cards cooled with LN2 or Phase change unit... with incredible OC...
Wihout the 8 pin you will not get the overdrive in CCC...

But there's perhaps an impact with the type and power of the PSU you use.. ( Watts and Ampers) if the 6+8 pins are not both connected..

Personally i have not see any issues... but it can be the case with some PSU with a lot of fluctuations on 12V... or with low Ampers/watts... difficult to be sure...

If you can... a good PSU is allways a must to have for OC.. Low PSU will allways limit an OC... So if you need or can change it, it's never a bad idea.

[antonfrompresto]

I have a decent PSU ready for a new build its an OCZ GameXStream 600W. I will be building this PC when intel drop their prices. I am hoping this PSU will be able to supply enough power for the PC which will have a Q6600 and HD 2900XT with a single hard drive. So the Q6600 and HD 2900XT will be the biggest power hogs but I thought that as I am going for a single GPU setup this PSU would be more than capable, am I wrong? And what is overdrive; is it overclocking via the official control panel?

[Lane-k]

It will depend of the OC of your CPU and GPU... My OCZ 850W is dead, i use know a Enermax 620W... if i OC my E6700@4.2ghz (1.65V bios).. and then OC the 2900 to more of 900 on core... i can't pass 3D06.. the PC crash and reboot.. or the screen freeze, and then i have a find message: GPU specifications have change... and driver have revert it to default settings.. ( something like that).. this will say the 620W is at his limit.. or there's not enough watts, or amp or both..

So for run all days.. no prob, for make some good bench run, it will be OK.. but if you will max OC then.. i don't think it will be enough..

[Sparky]

I'd say that the 600W OCZ should work, but for big overclocking the lower-amped multiple 12V rails (vs a single powerful 12V rail) on that unit might limit you.

[antonfrompresto]

Well I'm hoping to get a GO stepping Q6600 by phoning around after the price drops to try and find one. It will be 24/7 and will need to be totally reliable so I will probably not go beyond about 3.2GHz on the Q6600 and about 800/1800MHz on the HD 2900XT.

[cadaveca]

then you might need a better psu for quad overclocking and HD2900.

[antonfrompresto]

I'll probably go for either a 320MB or 640MB 8800GTS then as these require a lot less power don't they? I think even a 8800GTX uses less power than a HD 2900XT. Would I have any worries when overclocking both CPU and GPU with a Q6600 and 8800GTS with this PSU like it seems I would with the HD2900XT?

[cadaveca]

More than likely. the quad draws 130w/120w @ stock, and far more when overclocked. You'd need to confirm that both rails are seperate..ie. rail 1 is cpu/mobo only, rail2 is pci-e/devices only. If second pci-e connector uses same rail as cpu, any top-end card will have issues when paired with an overclocked quad.

[antonfrompresto]

I've had a quick search and believe this information to be true about the rails.

+3.3V(36A), +5V(30A), +12V1(18A), +12V2(18A), +12V3(18A), +12V4(18A)

+12V1 = CPU
+12V2 = Second CPU/Video card
+12V3 = Motherboards and Peripherals
+12V4 = Primary Video card

[cadaveca]

ah, so t should work @ 4 12v rails, but it WILL be a lmitingi factor when it comes to overclocking. That 18a is probably MAX rating, not MAX continuous...

Anyway, i was imagining only dual rail, not quad.

[antonfrompresto]

So this PSU will not be suitable for an overclocked Q6600 and overclocked 8800GTS or HD2900XT?

[Lane-k]

For begin... yur PSU should be enough... at the moment you don't try get a bench period with HIGH CPU and high OC on your GPU ( when i say High.. it's around 3.6-3.8ghz with a QX and HIgh OC on your GPU). all should be fine.. ( my Enermax is 620W . 2x12V rails @ 22A...) ... If then you see the PSU limit your OC.. buy a more powerful... like i have say higher.. a powerful PSU is allways a good way where put some money if you will high OC on your system.

[antonfrompresto]

For begin... yur PSU should be enough... at the moment you don't try get a bench period with CPU@ 4.3ghz and high OC on your GPU.. all should be fine.. ( my Enermax is 620W . 2x12V rails @ 22A...)

I would be quite happy with a 320MB or 640MB 8800GTS but definately want a G0 stepping Q6600 so would it be stable with a high 24/7 overclock of the CPU and GPU? The 8800GTS is a lot less power hungry than the HD 2900XT isn't it?

[ColonelCain]

Here's a fix to get 2x6 pin working for Overdrive:
Plug the 2x6 pin connectors in like it says in the manual. Then, for the remaining pins (that would be used with a 8-pin connector), use a paperclip or something, and bridge the 2 empty connectors. You now can overclock in overdrive! Good to go.

[antonfrompresto]

Alright as it should provide some future proofing I will see whether I can return my PSU as I only bought it for this build and it is still in the box. What do you guys reckon to this providing I can return the OCZ. Also do you reckon this PSU would fit in an Akasa Eclipse-62?
http://www.overclockers.co.uk/showpr...123&subcat=103

[NickS]

I know that the HD 2900XT has a 6 pin and 8 pin PCI-E socket. From what I have read it seems to run fine with two 6 pin PCI-E but I am unsure of whether there are any issues associated with using two 6 pin PCI-E. Will a HD 2900XT overclock as much as with the official 6 pin and 8 pin setup or would I have to settle for a more mild overclock if I had to go for the two 6 pin setup?

Thanks, Anthony

2x 6 Pin will overclock the same, and run the same.

[Lane-k]

Here's a fix to get 2x6 pin working for Overdrive:
Plug the 2x6 pin connectors in like it says in the manual. Then, for the remaining pins (that would be used with a 8-pin connector), use a paperclip or something, and bridge the 2 empty connectors. You now can overclock in overdrive! Good to go.

I was not knowing that.. he he.. thanks..

[cadaveca]

I would be quite happy with a 320MB or 640MB 8800GTS but definately want a G0 stepping Q6600 so would it be stable with a high 24/7 overclock of the CPU and GPU? The 8800GTS is a lot less power hungry than the HD 2900XT isn't it?

Yes. but...

18ax12v=216w.

MAX.

120w cpu @ 150%=180w.

MINIMUM.

That leaves you with 26w extra.

Problem is, cpu's power consumption is not a linear scale. Figure exponential growth, as you do not even get linear growth just increasing speed, nevermind voltage.

At stock, yes, this psu may be OK. it really depends on how it deals with the crossload you will apply(high 12v, low 5v/3.3v) as well.

[antonfrompresto]

So would I be right in saying that the Antec TPQ-850 TruePower Quattro 850W PSU would be no better for overclocking, despite being very powerful, because its same four 12V 18A rails would provide the same limiting factor.

+3.3V@25A;+5V@30A;+12V1@18A;+12V2@18A;+12V3@18A;+1 2V4@18A;-12V@0.5A;+5VSB@3.0A

+12V1 > EPS12V 8-Pin and ATX12V P4 connectors
+12V2 > 4-Pin Molex, SATA and Floppy connectors
+12V3 > Main ATX, 1x6-Pin PCI-Express and 1x 8-Pin PCI-Express connectors
+12V4 > 1x6-Pin PCI-Express and 1x 8-Pin PCI-Express connectors

[antonfrompresto]

So basically I need a powerful single rail for an overclocked Q6600 and HD 2900XT such as the PSUs in this thread?
http://www.xtremesystems.org/forums/...d.php?t=138129

I am thinking this would be suitable after reading that thread, would it provide plenty of headroom even when overclocked?
http://www.scan.co.uk/Products/Produ...oductID=565198

The rail specs of this PSU are here;
http://www.pcper.com/article.php?typ...&aid=423&pid=2

[cadaveca]

ok, so, lets dig into this a bit more.

so, first psu, 18a max, 4 rails, 600w.

18a=216w. 4x216w=864w.

Your psu cannot put out 864w..it's a 600w unit.

So you understand that that 18a rating is false, right?


Now, the antec unit...18a/rail, x4 =864w.

unit is 850w....probably 15a MAX oper rail on that one(real, i don't care what the label says).

15ax12v=180w.


This Antec may allow for 50% overclock.


Silverstone unit, well, it won't be a victim of the same issues, and should allow for good overclocking...


but...

because it is a single rail unit, transients(ripple) on the line will be large as all 12v devices draw from teh same source. transitions from idle to laod will ahve the largest impact on this unit, whne fully loaded up with a couple of vidcards and a quad, so you need a really good mobo that can deal with such a power source.