What Is Blockchain? How It Works, Explained in Plain English

A blockchain is a shared record book that many independent computers keep identical copies of, where each new page is linked to the last by a digital fingerprint, so edits show. The US National Institute of Standards and Technology (NIST) defines blockchains as “tamper evident and tamper resistant digital ledgers implemented in a distributed fashion.”

That definition sits underneath every coin you hold, including Bitcoin and XRP. Knowing how the record works tells you what it protects, what it doesn’t, and where the real weak spot is for a holder. This guide covers blocks, hashes, nodes, consensus, public and private chains, and the common claim that a blockchain “can’t be changed.”

What is a blockchain, in plain English?

A blockchain is a ledger, meaning a record book, that no single company or office keeps. Ethereum’s developer documentation calls it “a public database that is updated and shared across many computers in a network.” NIST’s 2018 report adds that it works “without a central repository,” so there is no master copy to edit or swap out.

Think of a class notebook where every student keeps an identical copy, and a new line only counts once the class agrees on it. In crypto, the lines are transactions: which address sent what, to which address, and when.

What is a block, and what is a hash?

A block is one page of the record book, holding a batch of transactions. Ethereum’s docs describe data “being stored in consecutive groups known as ‘blocks’.” A hash is the fingerprint that links the pages together.

NIST describes hashing as a method that “calculates a relatively unique output” from data of nearly any size. Three properties matter:

• The output is a short code of fixed length, whether the input is one word or a whole book.
• It only works one way. You can’t rebuild the page from the fingerprint.
• NIST says “Even the smallest change to the input (e.g., changing a single bit) will result in a completely different output digest.”

How does a blockchain link blocks together?

Each block stores the hash of the block before it. NIST says “Blocks are chained together through each block containing the hash digest of the previous block’s header.” The Bitcoin whitepaper, published in 2008 under the name Satoshi Nakamoto, put it this way: “Each timestamp includes the previous timestamp in its hash, forming a chain.”

Here is what that means for an edit. NIST says “If a previously published block were changed, it would have a different hash.” The next block still holds the old fingerprint, so the link breaks, and so does every link after it. That is the meaning of “tamper evident.” Ethereum’s docs make the same point: the data in a block cannot change without changing all later blocks, which would need the network’s agreement.

Who keeps the copies? Nodes, explained

The computers that keep copies of a blockchain are called nodes. Ethereum’s docs say “Nodes ensure everyone interacting with the blockchain has the same data.” NIST calls it a key benefit that “every user can maintain their own copy of the ledger,” and describes a full node as one that stores the entire blockchain and checks that transactions are valid.

Because many nodes hold the same record, a single altered copy stands out. Its fingerprints no longer match everyone else’s.

How do the computers agree on the next block?

Nodes agree using a consensus mechanism, a shared set of rules for deciding which block comes next. Ethereum’s docs say “To accomplish this distributed agreement, blockchains need a consensus mechanism.” Without one, two computers could add different next pages and the record would split.

Network	Consensus approach	How the next block is decided
Bitcoin	Proof of work	NIST: a user “publishes the next block by being the first to solve a computationally intensive puzzle” (mining)
Ethereum	Proof of stake	Validators lock up coins as stake, and stake helps decide who publishes new blocks
XRP Ledger	XRP Ledger consensus protocol	Validators agree on each new ledger version, which “builds on a previous ledger version” (xrpl.org); no mining

Different rules, same goal: one record that the whole network accepts. Our XRP Ledger explainer covers the XRP Ledger’s version in more detail.

What is the difference between a public and a private blockchain?

A public blockchain lets anyone take part, while a private one has a guest list. NIST says “In a permissionless blockchain network anyone can read and write to the blockchain without authorization,” while permissioned networks “limit participation to specific people or organizations.”

On a public chain, you can read the record yourself with a block explorer, a website that shows any address’s balance and transaction history. You don’t have to take anyone’s word for what an address holds. Our guide to reading an XRP transaction on XRPScan walks through one, field by field.

Can a blockchain be changed?

Yes, in some situations, but it is very hard to do without the network noticing. NIST says calling blockchains immutable “is not strictly true,” and that they “cannot be considered completely immutable, because there are situations in which the blockchain can be modified.”

NIST gives two examples:

1. Tail blocks can be replaced. On some chains, the most recent blocks can be swapped out by a longer competing chain. That is why many users wait for several more blocks before treating a transaction as settled.
2. A 51% attack. On permissionless chains, an attacker holding more than half of the resources used to make new blocks could push through an alternate chain.

The cost rises with age. The Bitcoin whitepaper says “To modify a past block, an attacker would have to redo the proof-of-work of the block and all blocks after it.” NIST adds that, depending on the network’s size, such an attack can be very costly. So the accurate version is: hard to alter, not impossible.

What does a blockchain mean for your money?

Your coins are entries in this shared record, tied to an address. A private key is what lets someone write the next entry for that address. NIST is direct about the risk: “If a user loses a private key, then any digital asset associated with that key is lost.” The record is hard to fake, but the key is the weak spot. Our seed phrase explainer covers how that key is usually backed up.

Two more limits are worth knowing:

• The chain records mistakes faithfully. A send to the wrong address is recorded as firmly as a correct one. NIST also notes that when real-world information is entered, “Humans could record false information (intentionally or unintentionally),” and the chain can’t tell.
• The record doesn’t create value. NIST says of the technology: “It is not magical; it will not solve all problems.” A blockchain records who controls what. Whether any coin is worth anything is a separate question. Our plain-English guide to cryptocurrency covers that bigger picture.

Blockchain basics checklist

Use this to check your own understanding, and your own setup:

Idea	Plain-English version	What to do with it
Ledger	A shared record book, copied on many computers	Know that no single company holds the master copy
Block and hash	Pages linked by fingerprints	Treat confirmed history as hard to change
Nodes and consensus	Copies plus shared rules for the next page	Know which consensus your coins use
Public vs private	Open to anyone vs a guest list	Use a block explorer to read public records yourself
Immutability	Hard to alter, not impossible	Wait for confirmation before treating a payment as final
Keys	The key controls the entry	Write down who holds the key to each coin you own

What to check next

Look up one of your own addresses on a block explorer for its network. Confirm the balance and history match what you expect. Then list each holding and note who holds its key: you, or an exchange. Those two steps turn the theory above into a clear picture of what the record says about your money.

Sources

• NIST IR 8202, Blockchain Technology Overview (October 2018)
• Satoshi Nakamoto, Bitcoin: A Peer-to-Peer Electronic Cash System (2008)
• ethereum.org, Intro to Ethereum (developer docs)
• XRP Ledger documentation, Consensus Protocol