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New build psu and sli setup - old school nub

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August 10, 2010 7:58:49 AM

Just to get a few things straight.  My last desktop PC was a few years ago, now.  Since then I have been using several laptops.

The last time I build a desktop, it had a Barton 2500+ oc'd to 3200+ spec and a Radeon X800 pro.  In those days, it was simple; plug in the mobo and the rest is molex.

My new build (already underway with ordering parts, but won't be assembled until the start of October) consists of the following:

Antec 1200 (bought; but interested in NZXT Phantom)
Nexus RX-8500 PSU (bought)
i7 930
2x gtx460 in sli
and other parts (single hdd, single optical drive, 6gb (3x2gb ddr1600) etc.

The gtx 460 each require 2x 6pin power connectors.  The PSU seems to come with 2x 6pin power in modular cables as well as 2x 6pin power attached with the main power lines.

My question (4 actually):

1.  The PSU has 4 PCIe 6pin outputs on the back of the unit.  I assume each of these is its own 12V rail.  Seeing as how the PSU only comes with 2 cables, would I use these 2 cables from say one rail into a single card and then use the 2 cables (non-modular) into the other card?

2.  I can't find 6pin to 6pin PCIe power cables anywhere!  Would I be able to buy a couple 6pin to 6+2pin cables and just leave out the +2 (not connected)?

3.  Would there be any benefit to using the modular 12V outputs (2x2 on the back of the PSU) only to power the 2 cards without using the non-modular 12V cables?

Here's a picture of the back of the supply pulled off a google image search.

More about : build psu sli setup school nub

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August 10, 2010 12:44:56 PM

1) You can use the 2 fixed PCI E cables to go to a card (you can leave out the +2 as your cards only have 6 pin). Then connect the modular cables to the PSU and connect to GPU.

2) Yes 6pin to 6+2pin work fine in a 6pin card (that is why they are called 6+2pin as opposed to 8pin and why the +2 are seperable to the 6) though you don't need to buy them as your PSU seems to have enough connectors.

3) No. The PSU just seems to be capable of dealing with a tri SLI set up. The advantage of a modular PSU is the ability to only use as many cables as you require, so using all 4 modular PCI E and leaving the 2 fixed ones idle inside your machine would defeat the purpose of it.

In general, a modular PSU always has the 20+4pin, 4pin and 8pin coonectors as fixed wires as these are not optional for running a PC. Of course, nowadays most modern GPU cards require two PCI E 6/6+2 cables (especially if you are using a powerful PSU, it suggests you have powerful cards) so it seems your PSU has decided that the PCI E cables are just as essential as the other connectors so have come with 2 fixed as well as the option to add more for SLI or Tri SLI.

So while it may be confusing for them to have modular PCI E slots and fixed ones, it just seems that the PSU manufacturers felt that PCI E cables were as essential as other parts so it made sense to at least have two as fixed cables (I guess it helps new people from accidently leaving their cards without extra power which sometimes happens - but if you have two cables dangling loose on a modular PSU it is a good hint that they are forgetting to connect something)
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August 10, 2010 2:34:24 PM

Ok, get a gtx 480 and then later down the line get another, never go with SLI first.
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August 10, 2010 2:55:19 PM

I usually support stronger card set ups. But 2 x GTX 460s give more performance for less money - the downside is of course you cannot easily upgrade from that as the GTX 480 can be doubled up later - that is why 2 card set ups are inferior...however, in this case I prefer the 2 x GTX 460s as it gives plenty oof power to last and more importantly the GTX 480 is the original Fermi design and is just a horrible card.

If going fro a single card set up I would wait and hope a redesigned GTX 480is released
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August 17, 2010 5:54:22 AM

I used to be of the idea that buying a single 480 would be better but since the performance gains of the two 460s are greater than the overall increased maximum load (idle is less according to what I've seen) power consumption, I would rather do the SLI 460.

The cost of 2 460 cards is roughly the same as a single 480. So instead of buying a single 480, I will buy 2x 460 and when they get old, just replace them both. Two cards may even hold their value better than one; although, that is entirely something I just made up right now. At that point, a single card may be a better alternative. I don't plan on ever (in the foreseeable future) doing more than 2 cards.

Thanks for the definitive response, asteldian.


Quote:

1. The PSU has 4 PCIe 6pin outputs on the back of the unit. I assume each of these is its own 12V rail. Seeing as how the PSU only comes with 2 cables, would I use these 2 cables from say one rail into a single card and then use the 2 cables (non-modular) into the other card?


Just to correct this statement, I meant to say that the 4 outs (2+2) are one 12V for each 2 outs.
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August 19, 2010 11:58:28 AM

Best answer selected by kevbodian.
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