Blockchain Basics
An append-only, distributed database maintained by a network of computers that uses cryptography to ensure data immutability.
While first conceptualized in 1991 by Stuart Haber and W. Scott Stornetta for cryptographically securing digital documents, the first widely deployed blockchain was Bitcoin, launched by the pseudonymous Satoshi Nakamoto in 2009 to solve the 'double-spending' problem in digital currency without a trusted central authority (like a bank).
Blockchains can be categorized into two main types:
1. Permissionless (Public): Anyone can join the network, read the ledger, and participate in consensus (e.g., Bitcoin, Ethereum).
2. Permissioned (Private/Consortium): Access is restricted to known, vetted entities, often used by enterprises for supply chain tracking or internal settlements (e.g., Hyperledger Fabric).
graph LR
Center["Blockchain Basics"]:::main
Pre_cryptography["cryptography"]:::pre --> Center
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Pre_distributed_systems["distributed-systems"]:::pre --> Center
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Rel_layer_1["layer-1"]:::related -.-> Center
click Rel_layer_1 "/terms/layer-1"
Rel_distributed_ledger_technology_dlt["distributed-ledger-technology-dlt"]:::related -.-> Center
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🧒 Explain Like I'm 5
Imagine a shared digital notebook that thousands of strangers keep a copy of. Whenever someone wants to write a new page (a [block](/en/terms/block)) of transactions, everyone checks to make sure the math is correct. Once they all agree, the page is glued into the notebook forever. Nobody can ever erase or change a glued page, and because everyone has their own copy, they instantly know if someone tries to cheat.
🤓 Expert Deep Dive
Cryptographic Chaining and Immutability
Blockchains achieve tamper-evidence through cryptographic hash functions (e.g., SHA-256). Each block header contains the hash of the previous block header, creating a strictly ordered linked list. The transactions within a block are typically hashed into a Merkle [Tree](/en/terms/merkle-tree), allowing efficient verification of specific transactions without downloading the entire block.
Consensus Mechanisms & Byzantine Fault Tolerance (BFT)
To maintain a synchronized state across a trustless, asynchronous P2P network, blockchains utilize consensus [algorithms](/en/terms/consensus-algorithms). Proof-of-Work (PoW) solves the Byzantine Generals Problem by attaching a thermodynamic cost (energy/hashing) to block creation, making Sybil attacks economically unviable. Proof-of-Stake (PoS) achieves this through economic penalties (slashing) for malicious validators.
Architectural Evolution
Early blockchains (like Bitcoin) were monolithic, handling data availability, consensus, and execution on the same layer. Modern blockchain architecture favors modularity (e.g., Rollups), separating execution from data availability to solve the scalability trilemma.
❓ Frequently Asked Questions
Are blockchain and cryptocurrency the same thing?
No. Cryptocurrency (like Bitcoin) is just one application built on top of a blockchain. Blockchain is the underlying database technology that makes cryptocurrencies possible.
Why can't blockchain data be changed or hacked easily?
Because the blocks are linked mathematically using hashes. If a hacker tries to change data in an old block, its hash changes, which breaks the connection to the next block. They would have to recalculate the entire chain faster than the rest of the network combined.
What is a 'node' in a blockchain?
A node is simply a computer running the blockchain's software. It keeps a copy of the ledger, validates new transactions, and communicates with other nodes to reach an agreement (consensus) on the true state of the network.