Blockchain Explained: How Distributed Ledger Technology Works

How Blockchain Works

A blockchain transaction goes through five steps. First, a transaction is broadcast to the network. A user signs the transaction with their private key, proving ownership. Second, nodes on the network validate the transaction by checking digital signatures and confirming sufficient balance. Third, valid transactions are grouped into a block. Fourth, the block is added to the existing chain through a consensus mechanism — proof-of-work (mining) or proof-of-stake (validation). Fifth, once added, the block is permanent. Changing a past block would require recalculating every subsequent block, which is computationally infeasible in a large network. This immutability is the foundation of blockchain's trust model. Explore Ethereum's smart contract platform →

Consensus Mechanisms

Proof-of-Work (PoW): Miners compete to solve complex mathematical puzzles. The first miner to solve the puzzle gets to add the next block and receives a block reward. PoW is extremely secure but energy intensive — Bitcoin mining consumes more electricity than some countries. The hash rate (computing power) of the network makes it practically impossible to reverse transactions. PoW is used by Bitcoin, Litecoin, and Dogecoin.

Proof-of-Stake (PoS): Validators lock up (stake) their own tokens as collateral. The protocol randomly selects a validator to propose the next block based on the amount staked. If the validator acts dishonestly, their staked tokens can be slashed (confiscated). PoS is energy efficient — Ethereum reduced its energy consumption by 99.95% when it switched from PoW to PoS in the Merge. PoS is used by Ethereum, Solana, Cardano, and many newer blockchains.

Delegated Proof-of-Stake (DPoS): Token holders vote for a small number of delegates who validate transactions on behalf of the network. DPoS is faster and more scalable than pure PoS but less decentralized. Used by EOS, Tron, and Steem.

Proof-of-Authority (PoA): A small number of approved validators run the network. PoA is used for private and permissioned blockchains where trust is established through identity rather than tokens. Used by enterprise blockchain platforms like Hyperledger. Learn the basics of cryptocurrency →

Types of Blockchains

Public (permissionless) blockchains: Anyone can read the ledger, submit transactions, and participate in consensus. No permission required. Bitcoin and Ethereum are public blockchains. They are fully decentralized but have scalability limitations — public blockchains typically process 7 to 30 transactions per second compared to Visa's 24,000.

Private (permissioned) blockchains: A single organization controls who can read, write, and validate. These are not truly decentralized but offer the benefits of blockchain — immutability, transparency among authorized parties, and efficient reconciliation. Private blockchains are used by enterprises for supply chain, internal record keeping, and intercompany settlements.

Consortium blockchains: A group of organizations shares control. Each organization runs a node, and consensus requires agreement from a majority of members. Consortium blockchains offer a middle ground between public and private. IBM Food Trust, which tracks food supply chains, is a consortium blockchain where Walmart, Nestle, and other food companies share data. Learn about decentralized finance on public blockchains →

Blockchain Applications Beyond Crypto

Blockchain technology is being adopted across industries for its core properties: transparency, immutability, and decentralization. Supply chain management is one of the most promising applications — companies can track goods from origin to consumer with timestamps that cannot be altered. Healthcare is another major use case: blockchain can store medical records in a secure, patient-controlled system that is accessible across providers. Digital identity systems allow individuals to control their personal data and selectively share it with companies or governments. Real estate title transfers can be recorded on a blockchain, reducing fraud and eliminating the need for title insurance. Voting systems built on blockchain could provide verifiable, tamper-proof election results. Smart contracts — self-executing code on blockchain — automate insurance claims, royalty payments, and lending agreements without intermediaries. Compare platforms to buy and trade cryptocurrencies →

What is the difference between blockchain and cryptocurrency?

Blockchain is the underlying technology; cryptocurrency is one application of that technology. Blockchain is a distributed ledger that records data in an immutable chain of blocks. Cryptocurrency is a digital asset that uses blockchain to record ownership and transfers. Think of blockchain as the operating system and cryptocurrency as an application that runs on it. Blockchain can be used for many purposes beyond cryptocurrency — supply chain tracking, medical records, digital identity, voting, and smart contracts. The confusion arises because Bitcoin, the first cryptocurrency, introduced blockchain to the world. However, blockchain technology has value independent of any cryptocurrency, and most enterprise blockchain applications do not involve cryptocurrency at all.

Can blockchain be hacked?

Blockchain technology itself is highly secure, but applications built on top of it can be vulnerable. The Bitcoin blockchain has never been hacked in over 15 years of operation. However, cryptocurrency exchanges (where users buy and sell crypto) have been hacked for billions of dollars. Smart contracts can have bugs that attackers exploit — the 2016 DAO hack on Ethereum stole $60 million through a code vulnerability. 51% attacks are possible on smaller blockchains where a single entity controls more than half the mining or staking power. The security of a blockchain depends on its consensus mechanism, the size of its network, and the quality of its code. Public blockchains with large miner or validator sets (Bitcoin, Ethereum) are extremely difficult to attack. Learn how to avoid crypto scams →

Is blockchain really immutable?

In practice, yes, but theoretically no. Immutability means that once data is written to a blockchain, it cannot be changed without controlling a majority of the network's computing power or stake. For large blockchains like Bitcoin and Ethereum, rewriting history would require an astronomical amount of energy or capital. However, blockchains can fork — if the community disagrees on a change, the chain can split into two separate chains (as Ethereum did with the Ethereum Classic fork). Private blockchains are less immutable because the controlling organization can alter the ledger. The immutability of a blockchain is proportional to the decentralization of its consensus mechanism. For most practical purposes, data on a major public blockchain is permanent.

What are real-world uses of blockchain beyond crypto?

Blockchain is being used for supply chain tracking (Walmart, Maersk, Nestle track products on blockchain), healthcare records (MedRec stores medical records on Ethereum), digital identity (Microsoft ION runs on Bitcoin), real estate title transfers (counties in California and Florida are piloting blockchain title systems), voting (West Virginia piloted blockchain voting for overseas military personnel), intellectual property rights (musicians and artists register copyrights on blockchain), and food safety (the FDA is exploring blockchain for drug supply chain tracking). These applications use blockchain for its transparency and immutability, not for cryptocurrency. Most enterprise blockchain projects use permissioned blockchains like Hyperledger or R3 Corda rather than public blockchains.

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