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Building computers for Bitcoin mining


CORSAIR Technical Marketing
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Bitcoin is becoming more and more popular. But because of this increase in popularity, the cryptographic puzzles that need to be solved in order to earn Bitcoins, an activity called "mining", have become more and more difficult. The problem with making the puzzles more complicated is that one requires more processing power to solve them and processing power requires electricity and electricity costs money! Fortunately, Bitcoin's value is currently very high. But it's very volatile as well. Currently, each unit is worth over $1000 USD. Only a month ago it was worth around $200 per unit. If one spends a lot of time and money mining for Bitcoins hoping for the $1000 per unit price, it's not unrealistic to fear that the price per Bitcoin may drop drastically. It's happened before. Back in April of this year, Bitcoin peaked at $238 USD per unit, only to have it dive down to $84 USD a week later.

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Bitcoins aren't actual coins, but you can buy tokens that represent your cyber-currency.

Some of you may have been living under a rock and are asking, "what is Bitcoin?" Bitcoin is a digital currency called "crypto-currency". It's not a physical currency and it's not controlled by any bank or government and isn't backed by any thing tangible with value, such as gold or silver. This has created a lot of skeptics and is one of the reasons behind Bitcoin's volatility. Despite this, Bitcoins can be exchanged for goods or even cash.

Initially a computer's CPU was used to crack the crypto puzzles, but with the increase in difficulty in the puzzles, it would take far too long to earn any Bitcoins. As the value of a Bitcoin unit increased, it began to make more economic sense to use multiple graphics cards to crack the puzzles. Specialized processors called "ASICs" (Application-specific integrated circuits) can be used for mining too and are much more efficient since they are programmed specifically to mine for Bitcoins, in some cases 100 times faster than a single graphics card. And while a ASIC that is 100 times faster than a graphics card doesn't tend to cost 100 times more than a graphics card, at thousands of dollars per ASIC it's still a very large initial investment into a PC made to mine for a very volatile crypto-currency, so many people still opt for using lesser expensive graphics cards for bitcoin mining.

Last month, Asrock introduced two new motherboards specifically for Bitcoin miners that want to use graphics cards to mine for Bitcoin. The motherboards feature 6 PCIe slots so users can install multiple graphics cards to use for solving puzzles.

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One of the PCIe slots is an x16 slot while the other five are x1 slots. You might be asking where one would find a graphics card that fits into a PCIe x1 slot. One can still use a typical x16 graphics card in all six slots of this motherboard, but will need an adapter like the one in the below picture:

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Regardless of whether the slots are x1 or x16, one would have to use adapters to install six graphics cards in one motherboard if you want to use graphics cards powerful enough to make mining worth while as most cards are dual slot (meaning they take up two slot spaces on the motherboard). You typically cannot run more than four graphics cards on one motherboard without "co-locating" the graphics cards away from the motherboard. The need to run graphics cards away from the motherboard has spawned a few creative chassis designs for Bitcoin mining machines. Some are mass produced specifically for Bitcoin mining machines like this unit from QDIY:

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Normally you would see a good 15 to 20% performance hit going from x16 to x1 PCIe slots, but that's when using a graphics card to render graphics and the extra bandwidth of the x16 slot helps move information from the graphics card to the CPU and RAM. When mining, each graphics card is like it's own little computer and there's relatively little information going back through the PCI bus. 
So now that you've spent this money on hardware, how much is it going to cost to run this thing? How about: A LOT!

When you play games on a PC, a second graphic card gives you better frame rates and the ability to turn on more eye candy or run higher resolutions. But two graphics cards doesn't mean twice the performance and twice the power consumption. But when you use graphics cards to mine for Bitcoins, each card works indecently of the others. So when testing with my GTX670s, which have a TDP of 170W, I was sucking down 145W from the power supply (gotta love Corsair Link!) FOR EACH CARD! I only have three cards ("only"? I know, right), but if I had six of them mining in that Asrock motherboard, I would need at least 870W just for the graphics cards. And that's assuming that I'm only going to use 145W per card based on the testing I did today. One would probably want to play it safe and actually size up the power supply with the TDP of the card. That means 1020W just for the graphics cards. Add to that another 120W for the motherboard, CPU, etc. and you're going to need one big power supply. Of course, you can get a Corsair AX1200i and power the whole thing and have the ability to monitor your power consumption as well. 

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But why skimp now and use mere GTX670s?  I only mention those because that's what I happen to use. The Radeon R9 290X is arguably the best card to use for mining. It performs better and is more efficient than other cards in its class. But even though it's efficient, that doesn't mean it doesn't use a lot of power. With a TDP of 250W, if you have six of these in the aforementioned Asrock board, you could require a PSU larger than 1600W!

So if you're going to get to mining, get in now since you never know how long these Bitcoin units are going to be up in the quadruple digits... and make sure you keep your power bill in check while you're at it!

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