Open Source FGPA Bitcoin MinerJust released was the Open Source FPGA Bitcoin Miner software. This miner allows bitcoins to be mined using a commercially available FPGA board.
FPGA boards consume much less electricity compared to GPUs for the hashing work performed when mining bitcoins.
FGPAs might have a MHash/J performance level around 20 or more whereas the most efficient GPUs are closer to about 2 MHash/J.
There are fears that FPGA mining will force miners using GPUs today to either pivot and switch to FPGA mining for their operations or to abandon mining completely when the efficiency disparity makes GPU mining uncompetitive.
Those fears are likely unwarranted just yet though. The cost of the equipment and not the cost of electricity continues to be the primary concern affecting miner’s decision on whether or not to add capacity.
Using commercially available FPGA boards to attain a certain level of hashing can require investment several times that required for a GPU-based equivalent.
Though a less costly FPGA board designed specifically for bitcoin could be built, there are no sources for such a product yet – at least not commercially.
It will likely be many months yet before the FPGA would even start to displace the GPU as the technology responsible for significant increases to the mining difficulty measure.
GPU miners have been able to reach the breakeven point, on a per-dollar invested basis, within a couple months after bringing new capacity online. Thereafter a decent profit continues to be returned though the profitability level can decline steadily with each subsequent increase in difficulty when there is no matching increase in the bitcoin exchange rate as well.
The Bitcoin network has continued to see capacity come online at an unprecedented and torrid pace – over 30 GHash/s of capacity was added each day during the most recent difficulty adjustment period, for example.
Because of the recent run-up in the bitcoin exchange rate mining is generally considered to be very profitable at the present time. It will remain highly profitable until either the exchange rate drops or the difficulty level increases significantly as the result of additional mining capacity being procured and brought online by miners seeking those profits.
With so many miners active now, the global supply of GPU hardware has become constrained. Even used GPUs found on eBay, for example, are becoming difficult to find. If the now-discontinued ATI HD 5870s and HD 5970s were still sold, or AMD were able to keep up with demand for the AMD HD 6990s, the difficulty increases would likely be even greater than what is being seen now.
Even though the FGPA solution is extremely expensive relative to its GPU equivalent, FPGAs are widely available commercially. If the bitcoin exchange rate were to spike further, FPGA mining may be about the only option for being able to add any significant amount of mining capacity.
The higher power efficiency that an FPGA provides is not just a factor for comparing the cost of electricity to mine but also when other factors are considered.
The total amount of electricity consumed by a miner with a GPU mining rig or two will add up quickly. Individual miners are already popping breakers after exceeding limits on the amount of current available from household circuits used when mining with multiple GPUs in a single rig even.
Those with multiple rigs are finding limits to the amount of electricity fed to the property as well. When power consumption limits are a constraint, then the FPGA with its significantly higher power efficiency might be the only method to increase mining hashing capacity.
Residential electric rates are often tiered to encourage conservation. As a result the incremental rate for mining starts at the most expensive tier for the household.
Individuals mining from their homes should be the biggest beneficiaries from having an efficient FPGA alternative but the equipment’s high cost will remain a major limiting factor, as will the technical skill level necessary for FPGA mining.
Further out, if the exchange value of bitcoin rises much further the numbers begin to approach the level where building and producing an ASIC design might become feasible.
If or when that happens, then the clock counting the days left for GPU mining can start ticking.
Written on 20 May 2011.