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I am considering setting up a new rig to mine ETH or XMR. To keep my costs are low, I am looking to bring my ASUS LGA775 P5Q-E motherboard out from retirement and slap it with an used low 45W TDP processor, 4GB retired DDR2 RAM and a 32GB SSD from Amazon. My retired PSU is a Corsair HX620 which is 80+ White certified. For the GPU, I have a Sapphire HD7950 Vapor-X currently but I am not sure whether to go for RX470 or RX480, whether to pick 4GB/8GB options. My electricity costs $0.15 kWh.

Some of my Questions

• Which are my most cost effective options? RX470 or RX480, 4GB or 8GB
• How many GPU can my PSU support now?
• How many GPU can my motherboard support? There are a total of 5 PCIe slots, both x16 and x1

Any insights would be awesome! I appreciate any advice the community can contribute.

You can find everything, here on the forum, it is NOT necessary to create another same thread everyday.
I'm sick of these lazy people. Give me everything on the plate, in front of my nose, right here, right NOW!!!
Do your fucking own research...

For your info, I AM searching on the forum and also on Ethereum community forum. Some answers are just not as straight forward given many variables but I have decided to go with a Sapphire/PowerColor RX480 8GB instead.

I am still not sure how much power 4-5 cards will require but pretty sure 620W 80+ Bronze won't cut it. Not sure if 1,000W 80+ Gold will be enough either since most posts touches on 6-GPU rigs.

Yes, I am doing my own fucking research and definitely not sitting around waiting for an answer. All I did was to ask for insights, it is up to individuals whether they had similar experiences to share or contribute to my learning.

The hx 620 is a single rail psu with 3x 18 amps @ 12V virtual rails (each 12V rail is over current protected @18A = 216W). (have a look at the sticker).

Each PCIe slot needs at least 75W @ 12V (6.25 amps). So my guess is, you are good with 3 RX480/470s. If your psu can handle >225 watts per rail than four cards, but I wouldnt recommend it for 24/7 usage.

Which card you are gonna use is absolutely your choice.

With powered risers, every slot should work fine, if it isnt shared with some onboard stuff -> have a look in the manual for that.

Edit: Here (http://www.hardwaresecrets.com/corsair-hx620w-power-supply-review/9/) is the test. They managed to squeeze 670 Watts (@12V) out of it. So with 4 RX 480 cards it is maxed out and sucks 900 Watts at the wall.

I don't know about rails and that kind of things but I can help you with your GPU choice. The main questions are : is it for long-term or short-term and are you going to resell the cards in some times to get your ROI back or not.

That's some really interesting insights for my PSU. I guess I will have to consider a 80+ Gold 1,000W PSU to power 4-5 cards. I am buying powered risers for the 2 PCIe x1 slots and 1 of the PCIe x16 slots. My concern is mainly about conflicts with onboard components as well. tThe manual did not mention much except for a warning about conflict.

Currently, it is still somewhat vague as POS is likely to come next year for ETH. Unless I can find an altcoin to mine profitably, I may eventually sell off some of the cards to recoup on the initial investment. At the same time, I can get the cards relatively cheaper from Amazon compared to what I am getting locally or from NewEgg.

If you count reselling it later, you should consider the 8 Go version that is only about 60$ more pricy but it will keep an higher value for a longer time since you will be able to resell it to gamers some day.

That's my thinking given the small difference with between reference/non-ref and 4GB/8GB.

I agree with flikflak in that your PSU should be able to support 3 RX470's comfortably even at stock settings. With BIOS mods you could possibly get 4, but you would really be pushing it. My personal comfort zone is to only run a PSU at ~80% of its rating for 24/7 use, so using this guideline would net you about 500 usable watts.

At stock settings you would be using about 450-475 watts with 3 x RX470's. BIOS mods could drop this down to about 380 watts giving you just about enough headroom to add a 4th card, which would bring the total to around 520 watts or so. A bit higher than I would like to see, but considering you already own the PSU you could do some tests with three cards at first to see where you are at.

Get a Kill-a-watt or similar meter that can measure the peak wattage over say a 24 hour period "at the wall" to get a good idea of what you real wattage usage is. This will vary over the course of the day as heat and fans ramp up and down, so you just don't want to base all your math with a low reading you might get when your first start-up.

Use atleast DDR3 RAM