Bitcoin Miners Explained: ASICs, Solo Mining and "Lottery" Miners

Key takeaways

• A Bitcoin miner is a specialized machine, an ASIC, that repeats the SHA-256 hash calculation as fast and as efficiently as it can while searching for a valid block.
• Mining moved from ordinary processors to graphics cards, programmable chips and then ASICs, first released in 2013. General-purpose hardware cannot compete with them today.
• Efficiency, the energy a machine needs per unit of hashing, decides how long it stays worth running. Heat, noise and power draw come with every machine.
• A solo miner keeps a whole block reward but may wait years or never win. A pool pays smaller, steadier shares for the same average income, minus a fee.
• “Lottery” miners are small devices that mine solo for a very small chance at a full block. Treat them as a hobby, and check the risks before buying any machine, new or used.

What is an ASIC miner?

An ASIC miner is a machine built around chips that do only one thing: compute the SHA-256 hash calculation that Bitcoin mining uses. ASIC stands for application-specific integrated circuit, a chip designed for a single task instead of general computing. The box around the chips holds a power supply, a controller that talks to the network and fans that push the heat out.

Because the chips contain no circuitry for anything else, they do that one job far faster, and with far less energy per calculation, than a computer, a phone or a graphics card. The flip side is that a machine built for SHA-256 cannot be repurposed, so its resale value depends on how it compares with newer models. Inside a Bitcoin Mining Operation shows how large sites run them.

How did mining move from CPUs to ASICs?

Mining moved to more specialized hardware because each step let a miner make more attempts for the same energy, and those who stayed behind earned less than they spent. The dates below are approximate, since each changeover was gradual.

Each new ASIC generation has generally been more efficient than the last, which keeps pushing older machines out. Hardware manufacturing is concentrated in a small number of companies, which critics see as a centralization concern.

What does a mining machine actually do?

A mining machine builds a candidate block header, runs it through SHA-256 twice and checks whether the result falls below the difficulty target. Almost every attempt fails, so the machine changes a number in the header and tries again. There is no clever puzzle-solving, only a brute-force search. Bitcoin Hash Rate and Mining Difficulty Explained walks through a small version you can try yourself.

The work comes from a pool’s server or, for a solo miner, from the miner’s own node. A hash that clears a pool’s easier target counts as a share, and one that clears the full network target is a block. The machine does not hold coins or set rules. Nodes enforce the rules, as What Is a Bitcoin Node? explains, and they reject a block that breaks them however much work went into it.

How is a miner’s efficiency measured?

Efficiency is the energy a machine uses for each unit of hashing work, usually quoted in joules per terahash, and lower is better. Two machines can have the same hash rate and earn the same revenue, yet the less efficient one pays a bigger power bill. That is why the oldest models are the first to switch off when margins shrink.

This article gives no figures, because models change every year. The maker’s specification sheet lists hash rate and power draw, and Is Bitcoin Mining Profitable? turns those into a break-even electricity price.

What do power, heat and noise mean in practice?

Nearly all the electricity a mining machine draws leaves as heat, so it behaves like a space heater with a very loud fan. Machines run around the clock, and many models draw as much as one or more space heaters running nonstop, which is why circuit capacity matters. Most people keep them out of living areas, and large operators use ventilation, water cooling or immersion in a non-conductive fluid. How to Mine Bitcoin at Home lists the practical checks, and Bitcoin’s Energy Use covers the wider debate about all this electricity.

What is the difference between solo mining and pool mining?

Solo mining means mining on your own and keeping the whole block reward if you find a block, while pool mining means combining hash power with others and receiving a share of each reward. Before fees the average income is the same, and only the timing differs.

A solo win pays the subsidy plus the fees in that block, and the new coins cannot be spent until 100 more blocks have been added. Bitcoin Mining Pools Explained covers payout schemes, fees and what to check before joining one.

How likely is a small solo miner to find a block?

Very unlikely in any given year, though never impossible. The network finds about 144 blocks a day, roughly 52,560 a year, and your chance on each one equals your share of the network’s hash power.

Take an invented example. Suppose a small device held one-billionth of the network’s hash power. It would be expected to win about once in 19,000 years, a chance of roughly one in 19,000 each year. Luck has no memory, so a miner that has gone a year without a block is no more “due” than one that has gone a week. How Long Does It Take to Mine a Bitcoin? has a longer table of invented shares.

What are “lottery” miners?

Lottery miners are small, low-power mining devices that mine solo, hoping for the slim chance of finding a whole block. They are sometimes sold as “mini bitcoin miners”. They often fit on a desk, make little noise and cost little to run, because their hash power is a tiny fraction of an industrial machine’s.

If one wins, the owner keeps the full reward, which is large compared with the device’s price. Most owners will never see that, and the electricity and purchase price are costs whether or not a block arrives. For many small devices the expected earnings, the average over all outcomes, are lower than those costs, so the buyer is mostly paying for the ticket. Learning how mining works is a fair reason to buy one if the money is not needed.

Be wary of listings that promise steady daily income from a small device, because solo mining does not work that way. Bitcoin Mining Apps and Cloud Mining covers phone apps and rented hash power, where the same promises appear.

What should you check before buying a used miner?

Assume a used machine has had a hard life, because it was probably run flat out for years. A low price is not a bargain if the model costs more in power than it earns.

• Wear and hidden faults. Fans wear out and chip boards fail or get repaired. A dashboard screenshot can be edited, so prefer a seller who lets you watch the machine run and offers returns or a warranty.
• Efficiency. Look up the model’s rated hash rate and power draw and run the break-even sums at your own electricity price before paying.
• Firmware. Unknown firmware may charge a hidden fee or send part of your work elsewhere. Reinstall the maker’s firmware, change the default password and enter your own pool and payout details.
• Seller risk. Prices far below the market, requests for payment in crypto or gift cards and a seller who disappears after the sale are classic warning signs, as Common Bitcoin Scams and How to Spot Them describes.

How do the halving and difficulty change the economics?

The halving cuts the block subsidy in half every 210,000 blocks, about every four years, so a machine earns half as much new bitcoin for the same work unless fees, the price or its efficiency make up the gap. Since April 2024 the subsidy has been 3.125 bitcoin. What Is the Bitcoin Halving? lists the dates and rewards.

Difficulty is a separate adjustment. Every 2,016 blocks it rises if machines have joined and falls if they have left, so each machine’s slice of a fixed prize shrinks as the network grows. Neither changes the ten-minute pace of blocks.

For a solo miner the prize per block is smaller after a halving, and each rise in difficulty trims an already tiny chance.

Spending on mining equipment is a financial decision, so talk to a qualified financial or tax professional first. New to Bitcoin? The Start Here path covers the basics in order.

Where to go next

• How to Mine Bitcoin at Home: What You Need and What to Expect: the setup steps, practical limits and safer alternatives.
• Is Bitcoin Mining Profitable? What Decides the Outcome: the revenue, costs and break-even sums.
• Bitcoin Mining Pools Explained: How Miners Share the Work and the Reward: payout schemes, fees and solo mining.
• Bitcoin Mining Apps and Cloud Mining: Do They Work or Are They Scams?: the red flags behind “free bitcoin” offers.