Proof of Work
Proof of Work is evidence that work has been done. An asic runs through candidates until it finds a hash below the target, and the candidate it finds gets verified instantly.
What Proof of Work is
The task is set up so that the only way to solve it is by brute force, while checking the solution takes a single calculation. The whole construction follows from that: hard to find, easy to confirm, nothing to fake it with. These calculations leave no useful byproduct behind, and that is the point of the scheme rather than a flaw in it.
The work costs electricity, and that is what makes the history of the network expensive to rewrite. To undo an old block you would have to redo all the work that came after it and outrun everyone else. The protection here is economic rather than mathematical: an attack costs more than it brings in.
Difficulty adjusts itself. New hardware arrives, blocks start turning up more often, and the network raises the bar to bring the interval back to normal. In bitcoin that happens every 2016 blocks, which is roughly once every two weeks.
There is another scheme as well, Proof of Stake, where the right to write a block comes from coins put up as a stake rather than from energy spent. Asics have no place there at all, so for us it is a neighboring universe: Ethereum moved over in 2022, and the hardware built for it lost its value within months.
Quick reference table
| What it proves | that the work really was done |
| Finding a solution | brute force only |
| Checking a solution | a single calculation |
| What the protection rests on | the cost of electricity |
| Difficulty retarget in bitcoin | every 2016 blocks |
What this means in practice
Your income is your slice of the total work of the network rather than the absolute speed of your asic. Network hashrate grows, and your slice falls at the same terahashes.
Overclocking adds work and with it the electricity bill. It makes sense only where the gain in hashrate outruns the gain in watts.
Changing the algorithm means changing the trade the hardware works in. An asic built for SHA-256 will not retrain for Scrypt, so the algorithm gets chosen before the purchase rather than after.
An example of the logic
An asic at 200 TH/s makes about 200 trillion attempts a second and throws away almost all of them: only a hash below the target is any good. When one turns up, any node on the network satisfies itself of that in a single check. All your revenue is payment for brute force that nobody else has a use for.
Related terms
Where to go next on the site
Algorithms
Coins
- Bitcoin coins
Hardware
- ASIC Miner knowledge base
Questions and answers
Can these calculations be pointed at something useful
No, and that is the point: the task is deliberately useless, which is what makes it impossible to fake and easy to check. A useful task would break the checking.
Why does difficulty grow while the reward does not
The reward is set by the schedule of the network, and difficulty depends on how much hardware is plugged in. These are two independent quantities, and the coins per terahash come out lower.
What happens to asics if a network moves to Proof of Stake
They become useless for that network. That is how it went with Ethereum in 2022, when the hardware built for it lost its value within months. The plans of a network get looked at before a purchase alongside the hardware figures.
How the terms connect
Every link in the chain is clickable. Orange marks where you are now.
Looking for an ASIC miner
The catalog holds 212 models. You can compare them by hashrate and by joules per terahash, then plug your own rate into the calculator and see what stays in your pocket.
Page written and checked by Denys Klimchuk. Updated .