Proof of Capacity (PoC), also called Proof of Space, is a consensus mechanism, where miners can use their hardware space to validate blocks in a blockchain.
Since Bitcoin got released in 2009, people developed new and better mining options besides Proof of Work. Proof of capacity is one of these new options that solve one big problem of Proof of Work: energy consumption.
Proof of Capacity is very similar to Proof of Work (PoW) but uses hardware space as mining power.
In the Proof of Work (POW) consensus algorithm, miners compete against each other and try to find a valid hash value to get a reward for finding a new block. To act like this, a miner has to solve a complicated mathematical problem as fast as possible. This consumes a lot of energy. This approach works like a lottery ticket system, where you try over and over again until you get the correct result.
The Proof of Capacity protocol allows miners to use empty hardware space to mine cryptocurrencies. Instead of searching permanently for the right result, like in Proof of Work, Proof of Capacity works by storing a list of right solutions on a hard drive before you start mining. The larger the hard drive space, the higher your chance that you have the right solution.
Before anybody could start mining, the hard drive has to be plotted. The plotting process creates a list of nonce values on your hard drive. A nonce contains 8192 hashes, which are numbers from 0 to 8191. All hashes are paired into scoops. For instance, hash 0 and 1 constitute to scoop 0, hash 2 and 3 constitute to scoop one, and so on.
After the plotting process, a miner could start mining. During this time, a miner calculates a scoop number.
For example, a miner starts with scoop number 38. The miner then would go to scoop amount 38 of nonce one and use that scoop’s data to calculate a deadline. The miner repeats that process for each nonce until no one is left. Of all calculated values, he chooses the one with the lowest result. This result is called a deadline.
A deadline represents the duration of time in seconds that have to pass since the last block was mined before a miner is allowed to mine the next block. If no one else has forged a block within this time, the miner wins and earns the rewards.
For example, if miner X comes up with a deadline of 30 seconds and no other miner can forge a block within 30 seconds, X will forge a new block and earn rewards for it.
Burstcoin is a coin that uses the Proof of Capacity concept.