At first, miners could only use their central processing unit (CPU) to mine, but this was not very power efficient and bogged down the system resources of the host computer. Miners then moved on to using the graphical processing unit (GPU) in computer graphics cards as they were able to hash data much faster than CPU's, around 50x to 100x, and this required less power. Eventually, the Bitcoin mining industry recognized the need for special equipment and this led to the development of field-programmable gate arrays (FPGA's). These FPGA's were specialized machines that repurposed existing technology and attached to computers using a USB connection while using much less power during mining than GPU's and helped to free up system resources on their host computers.
Today, application-specific integrated circuit (ASIC) miners are the new wave in the evolution of mining Bitcoin. These ASIC machines mine at unprecedented speeds, from 5GH/s to 1,500 GH/s, while consuming much less power than FPGA or GPU mining rigs, but are only available from a few manufacturers such as Butterfly Labs and Avalon at this time.
Butterfly Labs produces the most cost-efficient and power-efficient mining hardware in the industry available for both entry-level miners and experienced miners alike. Their smallest model, the Bitforce ASIC SC 5GH/s model is priced at $274 and is a great choice for those just getting started mining Bitcoin because they offer greater speed and reduced power consumption as opposed to GPU and FPGA mining. Additionally, Butterfly Labs offers a vast array of ASIC miners that include a 25GH/s, 50GH/s, and an unprecedented 1,500 GH/s model.
For more information go to: www.butterflylabs.com.
Avalon also produces ASIC miners that run at speeds greater than 65 GH/s and use a modular case system that allows users to add another 20 GH/s at a later time. However, they release their machines in batches and their machines use more power than the Butterfly Labs machines running at similar speeds. At this time, all ASIC miners produced by Avalon have been reserved and there is no announcement on future availability.
For more information go to: http://launch.avalon-asics.com/#home