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A distributed ledger is a database that is replicated and synchronized across many independent computers called nodes.

There is no single master copy — every node holds the full ledger and helps keep it consistent.

A traditional ledger lives on one server controlled by one party. A distributed ledger removes that single point of control and failure.

• Centralized: one owner, one copy, one trust anchor
• Distributed: many peers, many copies, shared trust

A node is any computer running the blockchain software and storing a copy of the ledger. Nodes connect directly to each other as peers in a network.

There is no central server to ask — peers gossip data among themselves.

Replication means every full node keeps an identical copy of all blocks.

If many nodes go offline, the data survives on the rest. This redundancy gives blockchains their famous resilience.

The ledger represents a shared state — for example, every account balance. All honest nodes must agree on this state.

When a new block is applied, each node updates its state the same way, so they stay in sync.

When you submit a transaction, your node broadcasts it to its peers, who relay it onward. This gossip protocol spreads it across the whole network in seconds.

Pending transactions wait in a pool called the mempool.

Because anyone can propose blocks, nodes need a way to agree on a single version of history. This is the job of a consensus mechanism.

Consensus ensures all honest nodes converge on the same ordered chain of blocks.

Distributed ledgers are often called trustless — not because trust is absent, but because you do not need to trust any single party.

You trust the protocol and the math (hashing, signatures, consensus) instead of an intermediary.

Ledgers differ in who may join:

• Permissionless (Bitcoin, Ethereum) — anyone can run a node
• Permissioned (enterprise chains) — only approved participants

Both are distributed, but they differ in openness and trust assumptions.

Because copies live everywhere and no one controls them all, distributed ledgers resist censorship and downtime.

Shutting one node down does nothing; the network simply routes around it.

A distributed ledger is a replicated, peer-to-peer database where nodes maintain a shared, agreed-upon state.

Replication gives resilience, gossip gives reach, and consensus gives a single source of truth without a central authority.

Test your understanding of distributed ledgers.

You learned that:

• A distributed ledger is replicated across many peer nodes
• All nodes maintain a shared state
• Transactions gossip across the network
• The system is trustless and resilient
• Consensus keeps everyone on one chain

Next course: how consensus actually works.