Encyclopedia Bitcoin basics · Entry 377

What is a blockchain, and what does Bitcoin’s actually record?

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Theme: Bitcoin basics
Sources: 7 cited records
Reading time: About 9 minutes
Automated verification: 2 October 2026
Substantive update: 2 October 2026

In this article

At a glance

Key facts

Key facts for What is a blockchain, and what does Bitcoin’s actually record?
Fact	Detail	Source
What links blocks	Each block header holds the hash of the previous block’s header	[4][1]
Block header	80 bytes, six fields	[4]
First block	Block 0, timestamped 3 January 2009, with a newspaper headline in its text	[5][6]
Target pace	About one block every ten minutes, re-tuned every 2,016 blocks	[3][6]
Idea’s origin	Linked timestamping, Haber and Stornetta, Journal of Cryptology, 1991	[2][1]
The word	The white paper never uses “blockchain”; it describes a “chain of hash-based proof-of-work”	[1]

A blockchain is a ledger written in batches, each sealed to the last

Start with the plain word. A ledger is a list of who paid whom. A blockchain is a ledger written in batches, called blocks, where each block carries a fingerprint of the block before it. The fingerprint is a hash: a short string computed from the block’s contents by a fixed mathematical recipe, such that changing even one character of the input changes the output completely. Because every block contains the previous block’s hash, the blocks form a chain, and the chain has a direction: older toward the start, newer at the end.

In Bitcoin the part that gets linked is the block header, a compact summary of 80 bytes. The developer reference lists its six fields: a version number, the hash of the previous block’s header, a single hash that summarizes every transaction in the block (the merkle root), a timestamp, a compact encoding of the difficulty target, and a nonce, meaning a number miners change while searching for a valid block. That is the whole thing. The transactions themselves hang off the header through the merkle root.

The white paper describes the effect in one sentence: each timestamp “includes the previous timestamp in its hash, forming a chain, with each additional timestamp reinforcing the ones before it.” Reinforcing is the right word. A block that is ten blocks deep is not just old; it is buried under ten more sealed batches, each of which would have to be redone to alter it.

The idea is older than Bitcoin: it started as a way to timestamp documents

Bitcoin did not invent the hash chain. The white paper’s section on the timestamp server cites work by Stuart Haber and W. Scott Stornetta, whose paper “How to time-stamp a digital document” appeared in the Journal of Cryptology in 1991. Their problem had nothing to do with money: in a world where every document is digital and easy to edit, how do you prove when something was written?

Their abstract puts the goal precisely. They wanted procedures that make it “infeasible for a user either to back-date or to forward-date his document, even with the collusion of a time-stamping service,” while keeping the documents private and requiring “no record-keeping by the time-stamping service.” The method was to hash each document and link the hashes, so that every certificate depends on the ones before it. A cheat would have to forge not one record but the whole sequence after it.

What Bitcoin added was a way to do this without a company running the service. The white paper says a timestamp server works by hashing a block of items and “widely publishing the hash, such as in a newspaper or Usenet post.” Bitcoin replaces the newspaper with a network of computers, and replaces the trusted publisher with proof of work, a cost that anyone can verify and nobody can fake.

Bitcoin’s chain records payments and proof of work, and very little else

People imagine a blockchain storing all sorts of things. Bitcoin’s stores a narrow set. Each block holds a list of transactions, and the developer guide is specific about the first one: it “must be a coinbase transaction,” the one that creates the block’s new coins and collects its fees. The rest are ordinary payments: references to coins someone received earlier, and instructions on where they go now. The chain tracks coins as spendable outputs rather than as account balances, which is why the site’s UTXO explainer matters if you want to read the ledger yourself.

The chain does not store names, and it does not keep an account for you. What it stores is the sequence: this block came after that one, this payment spent those outputs. The developer guide adds a practical rule that follows from the structure: the new coins in a coinbase transaction “cannot be spent for at least 100 blocks,” because a block near the tip of the chain could still be replaced.

The very first block shows how little a block needs to contain. Block 0, with a timestamp of 3 January 2009, holds one transaction, and its text field carries a newspaper headline from that day, “Chancellor on brink of second bailout for banks,” which is still hard-coded in Bitcoin Core’s source. The next block did not arrive for six days. That is the entire beginning of a record that has been extended, block by block, ever since. The site’s genesis block page goes through it line by line.

Rewriting the past means redoing all the work since

Linking blocks by hash makes tampering detectable. Making it expensive is the job of proof of work. To add a block, a miner must find a header whose hash falls below a target set by the network, which takes a great deal of trial and error; the developer guide describes the target as a value the header hash “does not exceed.” The white paper draws the consequence: once that effort has been spent, “the block cannot be changed without redoing the work,” and because later blocks are chained after it, changing an old block “would include redoing all the blocks after it.”

The network keeps the pace steady. Every 2,016 blocks, the software compares the time those blocks took against an ideal of 1,209,600 seconds, two weeks, and adjusts the target so that blocks keep arriving about every ten minutes. The difficulty adjustment is why Bitcoin’s block rate has stayed roughly constant while the hardware behind it changed beyond recognition.

Rules matter as much as work. Nodes, meaning computers running the Bitcoin software and checking everything for themselves, accept a block only if every transaction in it is valid and not already spent. A chain with more work behind it but an invalid block in it is simply ignored. That is why the site’s dossier on how Bitcoin’s blockchain works spends as much time on validation as on mining.

The buzzword and Bitcoin’s chain are different things

The word “blockchain” came later than the thing. The white paper never uses it. It speaks of a “chain of hash-based proof-of-work,” of blocks, and of the “longest proof-of-work chain.” The term became a category of its own in the decade that followed, applied to bank pilots, supply-chain databases and products that share little with Bitcoin beyond the name.

The US National Institute of Standards and Technology tried to pin the generic term down in a 2018 overview, defining blockchains as “tamper evident and tamper resistant digital ledgers implemented in a distributed fashion” and usually without a central authority. That definition is broad on purpose. It fits a private ledger run by a consortium of companies as well as it fits Bitcoin, and the two behave very differently in practice.

The difference is who can write and who can check. Bitcoin’s chain is public: anyone can read it, anyone can run a node to verify it, and adding a block costs real work that anyone can audit. A “blockchain” run by one organization with a short list of approved writers is a database with a hash chain attached. That may be useful, but it does not get Bitcoin’s properties. When someone says blockchain, it is worth asking which one they mean and who is allowed to add to it.

Direct answers

Questions people ask

Is blockchain the same thing as Bitcoin?

No. Bitcoin is a specific network and currency; its ledger is one blockchain. The generic word covers many systems, some public and some run by a single company, and the white paper that introduced Bitcoin never uses the word at all. It describes a chain of hash-based proof-of-work.

What information is stored on the Bitcoin blockchain?

Blocks of transactions, each with an 80-byte header that links to the previous block. The first transaction in every block is the coinbase transaction that creates new coins; the rest are payments that spend earlier outputs. There are no names and no account balances, only the sequence of transfers.

Can the Bitcoin blockchain be edited or deleted?

Not in practice. Every block carries proof of work, and each later block builds on it, so altering an old block means redoing its work and the work of every block after it, faster than the rest of the network keeps adding new ones. The white paper shows that chance shrinking exponentially with each added block.

Who invented the blockchain?

The linked hash chain comes from Stuart Haber and W. Scott Stornetta’s 1991 paper on time-stamping digital documents, which the Bitcoin white paper cites. Bitcoin’s contribution was to run that chain on an open network with proof of work instead of a trusted time-stamping service.

Inspect the evidence

The answer and key facts have stable claim links. These records retain the scope and qualification when reused.

A blockchain groups records into blocks that commit to earlier blocks through hashes. Bitcoin nodes validate transactions and select the valid chain with the most accumulated proof of work. Altering an earlier block changes its hash and breaks later commitments unless that work is redone. The records describe spending conditions and amounts, not necessarily the people behind them. Nodes can temporarily disagree about the tip, and pruned nodes need not retain every old block.