Bitcoin and Cryptocurrency Technologies

oards together, each with a 1 GH/s throughput, it would still take you about 50 years on average to
find a Bitcoin block at the early‐2015 difficulty level.
Figure 5.8: A home‐built rack of FPGAs. ​Although you don't see the cooling setup pictured here, a
rack like this would need a cooling system.
Despite the performance gain, the days of FPGA mining were quite limited. Firstly, they were being
driven harder for Bitcoin mining — by being on all the time and overclocked — than consumer grade
FPGAs were really designed for. Because of this, many people saw errors and malfunctions in their
FPGAs as they were mining. It also turned out to be difficult to optimize the 32‐bit addition step which
is critical in doing SHA‐256. FPGAs are also less accessible‐you can't buy them at most stores and
there are fewer people who know how to program and set up an FPGA than a GPU.
Most importantly though, even though FPGAs improved performance the cost‐per‐performance was
only marginally improved over GPUs. This made FPGA mining was a rather short‐lived phenomenon.
Whereas GPU mining dominated for about a year or so, the days of FPGA mining were far more
limited — lasting only a few months before custom ASICs arrived.
ASIC mining. ​Mining today is dominated by Bitcoin ​ASICs​, or​application‐specific integrated circuits​.
These are chips that were designed, built, and optimized for the sole purpose of mining Bitcoins.
There are a few big vendors that sell these to consumers with a good deal of variety: you can choose
between slightly bigger and more expensive models, more compact models, as well as models with
varying performance and energy consumption claims.
Designing ASICs requires considerable expertise and their lead‐time is also quite long. Nevertheless,
Bitcoin ASICs were designed and produced surprisingly quickly. In fact, analysts have said that this
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