Blockchain definition
A blockchain is a shared, append-only digital ledger that records transactions in linked blocks across a network of computers. Each block contains a cryptographic hash of the previous one, so past records are extremely hard to alter, and network participants agree on new entries through a consensus mechanism instead of relying on a central authority.
How does blockchain work?
Users submit transactions, such as transferring a token or updating a record, signed with their private keys. Nodes in the network validate these transactions against the rules, and a consensus mechanism, such as proof of stake or proof of work, decides which node proposes the next block and how others agree on it. Once added, the block links to the previous block through its hash, forming a chain that every full node stores and verifies independently.
Changing an old transaction would change that block's hash and break every link after it, so tampering is obvious and would require controlling a large share of the network. This gives participants a shared source of truth without trusting a single operator. Bitcoin, described in Satoshi Nakamoto's 2008 white paper, was the first widely used blockchain.
Types of blockchains
Blockchains differ mainly in who can read data, who can submit transactions and who can validate blocks. That choice shapes everything else, including performance, privacy, governance and cost, so it should be made early based on who needs to trust the system and why. The main categories are listed below.
- Public permissionless: anyone can participate, such as Bitcoin, Ethereum and Solana.
- Private permissioned: one organization controls participation, often for internal records.
- Consortium: a group of organizations shares control, common in trade finance and supply chains.
- Hybrid: private systems that anchor proofs or settle on public chains.
Blockchain use cases beyond cryptocurrency
Beyond digital currencies, blockchains are used for payments and cross-border settlement with stablecoins, decentralized finance applications, tokenization of assets such as funds and bonds, supply chain traceability, digital identity and verifiable credentials, and NFTs for digital ownership and ticketing. Enterprise frameworks such as Hyperledger Fabric support permissioned networks where several companies share records, for example tracking goods between manufacturers, shippers and retailers without one party owning the database.
Limitations of blockchain
Blockchains trade efficiency for decentralization. Public chains process fewer transactions per second than a conventional database, fees can rise during congestion, and data written on-chain is effectively permanent, which conflicts with privacy rules requiring deletion. Smart contract bugs can cause irreversible losses, and the ledger only guarantees what is recorded, not whether off-chain data entered into it was true. Regulatory treatment of tokens also varies by country and continues to evolve. Energy use is now far lower on proof-of-stake networks.
When does blockchain make sense?
A useful test: blockchain fits when multiple parties who do not fully trust each other need to share and update the same records, and no single party should control them. If one organization owns the data and users trust it, a traditional database is simpler, faster and cheaper. Nexzem's blockchain team starts every engagement by testing this question before recommending a chain, architecture or smart contract design. Often, a shared database with audit logs is enough.