Mining is one of the most misunderstood concepts in cryptocurrency. The word conjures images of physical extraction - which is deliberately evocative but not particularly accurate. Bitcoin mining is a computational process: computers compete to solve a mathematical puzzle, and the winner earns the right to add the next block of transactions to the blockchain and receive a reward of newly created Bitcoin. This process is the mechanism by which new Bitcoin enters circulation, by which the network achieves consensus without a central authority, and by which Bitcoin's security is maintained. Understanding it is essential for understanding Bitcoin's economics.
What Mining Is
When transactions are broadcast to the Bitcoin network, they sit in a pool of unconfirmed transactions called the mempool - memory pool. Miners are computers (specialised hardware called ASICs - Application-Specific Integrated Circuits) that collect these transactions, verify them against the protocol rules, and attempt to package them into a new block.
But adding a block to the blockchain is not free - it requires solving a computationally intensive puzzle called Proof of Work. Thousands of miners around the world are simultaneously competing to solve this puzzle. The first one to solve the puzzle broadcasts the new block to the network, the other nodes verify it, and if valid, it is added to everyone's copy of the blockchain. The winning miner receives the block reward.
The Proof of Work Puzzle
The puzzle that miners must solve is a specific type of hash function challenge. Recall that SHA-256 produces a unique hash for any input. The challenge is: find an input that produces a hash below a specific target value - a hash that starts with a certain number of zeros.
The only way to find such an input is trial and error - trying billions of different inputs per second until one produces a hash that meets the target. This is computationally expensive - it requires enormous amounts of electricity and specialised hardware. It is also trivially easy for any node to verify: they simply run the winning miner's solution through SHA-256 and check that the output meets the target. This asymmetry - hard to find, easy to verify - is the genius of Proof of Work.
Target: Find a hash beginning with four zeros (simplified example).
• Miner tries input: "Block data + 1"
• Output: 8f2a91c... (does not start with 0000 - try again)
• Miner tries: "Block data + 2"
• Output: 3b7f22d... (no - try again)
• Miner tries: "Block data + 458,291"
• Output: 0000a3f92b... (YES - starts with 0000!)
Broadcast to network. Every node verifies in milliseconds:
Run "Block data + 458,291" through SHA-256.
Output starts with 0000. Valid. Block accepted.
In reality: Bitcoin requires many more leading zeros - representing quintillions of attempts per second globally.
The Mining Reward
The miner who successfully adds a block receives two types of income: the block subsidy (newly created Bitcoin) and the transaction fees from all transactions included in the block.
The block subsidy started at 50 BTC per block in 2009. Every 210,000 blocks (approximately every four years), it halves - an event called the halving. After four halvings: 50 → 25 → 12.5 → 6.25 → 3.125 BTC. The most recent halving occurred in April 2024, reducing the reward to 3.125 BTC per block. This scheduled reduction in new Bitcoin supply is a core part of Bitcoin's deflationary monetary policy.
The Difficulty Adjustment
If more miners join the network, blocks would be found faster than every ten minutes. If miners leave, blocks would be found slower. Bitcoin solves this with an automatic difficulty adjustment: every 2,016 blocks (approximately two weeks), the network calculates how fast blocks have been found and adjusts the difficulty target accordingly. If blocks were found too fast, it makes the puzzle harder. If too slow, it makes it easier.
This elegant mechanism ensures that the block time stays close to ten minutes regardless of whether the network has 100 miners or 1,000,000 miners. It also means that as Bitcoin's price rises and attracts more miners, the network becomes more secure - more computational power means a 51% attack becomes even more expensive.
Proof of Stake - The Alternative
Proof of Work is Bitcoin's consensus mechanism - but not all blockchains use it. Ethereum switched from Proof of Work to Proof of Stake in September 2022. Rather than competing through computational work, Proof of Stake validators are chosen to add blocks based on the amount of cryptocurrency they have locked up (staked) as collateral. The economic incentive is similar - honest behaviour earns rewards, dishonest behaviour risks losing the staked collateral - but the energy consumption is dramatically lower.
Bitcoin's community has deliberately chosen to maintain Proof of Work despite its energy cost - arguing that the physical expenditure of energy creates a real-world anchor for Bitcoin's security that Proof of Stake cannot replicate. This is one of the fundamental philosophical divisions between Bitcoin and most other cryptocurrencies.