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All About Bitcoin Mining: Road To Riches Or Fool's Gold?

FPGA- And ASIC-Based Mining Devices

FPGA-Based Mining Devices

In late 2011 and early 2012, innovative companies like Butterfly Labs, ZTEX in Germany, a grad student in China, and some individuals in the U.S. started offering FPGA-based mining devices. While most of these were based on the $100 Xilinx Spartan6-150 FPGA, the BFL design used an Altera FPGA, which the company sourced at a discounted price.

The Xilinx Spartan6-150-based mining boards achieved about 200 to 220 MH/s per FPGA, and sold for approximately $1 to $2.50 per MH/s.

Meanwhile, Butterfly Labs offered its dual-FPGA 830 MH/s Single for the very aggressive price of $600 (less than 75 cents per MH/s).

In mid-2012, BFL started to ship the so-called miniRig, a 25.2 GH/s mining device consisting of a PC tower-like case with nine intake fans on the left side of the chassis and nine exhaust fans on the right side. It contains as many FPGA boards as necessary to reach the nominal total hash rate of 25.2 GH/s. Typically, that's 17 or 18 boards with two FPGAs each. The Altera FPGAs on the miniRig’s boards are larger, more expensive chips than the ones on the Single’s board, operating between 650 and 750 MH/s each with significant variance.

Below: Half the boards of a FPGA-based miniRig, mining with cgminer.

ASIC-Based Mining Devices

Avalon

Avalon is the ASIC-based successor of Mr. Zhang’s FPGA-based Icarus device. The ASIC is a small, single-core, 110 nm chip. An Avalon rig consists of several hundred chips and achieves a hash rate of approximately 66 GH/s.

Butterfly Labs

Shortly after beginning to ship its FPGA miniRigs, Butterfly Labs announced the impending release of ASIC-based, 60 GH/s "SC Singles", as well as a 4.5 GH/s low-end product called "Jalapeno", and a 1,500 GH/s high-end product called the "SC miniRig". In order not to jeopardize ongoing sales of FPGA-based mining devices, BFL offered a trade-in-program where, upon the return of a BFL FPGA-based device, a customer would receive a full trade-in refund for a ASIC device purchase of twice the price, thus saving 50% of the ASIC-device’s purchase price.

Exactly 10 months after starting to take pre-orders for the ASIC-based machines, BFL commenced shipping the first device, a 5 GH/s device replacing the Jalapeno, but drawing about six times as much power. BFL admitted to missing the power specification of its 65 nm ASICs by an order of magnitude, essentially turning a would-be 8 GH/s ASIC (16 cores @ 500 MHz) into a 4 GH/s chip clocked at a mere 250 MHz.

ASICminer

ASICminer created a 130 nm ASIC for its mining pool, but have started to auction a few 10 GH/s boards and are in the process of commencing sales of a USB key-style 300 MH/s miner: the Block Erupter USB. While the auction of the former devolved into a bidding war that ended at the questionably-high price of 75 or 76 BTC per device, the USB keys are being offered at a fixed price of 1.99 BTC each.

Comparison of FPGA and ASIC Chips

Spartan6-150BFL SingleBFL miniRigAvalonBFLASICminer
TypeXilinx FPGAAltera FPGAFPGAASICASICASIC
Process45 nm45 nm (?)45 nm (?)110 nm65 nm130 nm
Hash Rate Per Chip210 MH/s415 MH/s650-750 MH/s280 MH/s4 GH/s300 MH/s
Power Draw15 W40 W35 W2.8 W30 W2.5 W
Efficiency (MH/s per W)141020100133120
US$ / MH/s1 to 2.50.750.6VariesVariesVaries
NotesTypically 1 to 4 FPGAs Per Board2 FPGAs Per Board2 FPGAs Per Board, 17 to 18 BoardsPriced In BTC (prices increase)BFL Anticipates A Slight Reduction In Power DrawPriced In BTC (prices increase)