What is a blockchain? How computers verify a shared transaction record

Blockchain is not just a technology for buying and selling coins. It lets many participants keep the same records and check new entries against agreed rules. The name can sound complicated, but a useful starting point is to ask who records the information and who checks it.

Terms worth knowing

• Transaction: An action submitted to a network, such as sending assets or running a program.
• Block: A bundle of records, including verified transactions.
• Hash: A fixed-length value derived from data. Changes to the data change its hash, helping reveal alterations to a record.
• Node: A computer that participates in the network by relaying or verifying records. Its role depends on the type of node.
• Consensus: The rules for deciding which records the network accepts as valid.

How does a transaction become part of the record?

On a public blockchain such as Ethereum, a transfer request is sent to the network. Participating nodes check signatures, balances and execution rules, and verify transactions included in blocks. Each new block connects to the previous one, so changing an earlier record makes it inconsistent with later records.

Pressing Send does not complete every step immediately. Inclusion in a block, enough confirmations and an exchange crediting a deposit can all take different amounts of time. That is why a wallet can say a transfer is complete before an exchange says the deposit has arrived.

Does a permanent record mean its contents are trustworthy?

Blockchain verifies records; it does not judge whether a business is sound. A record can still contain a mistyped address, a fraudulent token or information that does not match reality. Public chains show transactions associated with addresses, but do not always reveal who actually controls those addresses.

Decentralization also comes in degrees. Verification may be widely distributed while a service's interface or administrative powers remain concentrated in a few hands. When researching a project, check its operating permissions, how people participate in verification and its public documentation, as well as whether it uses a blockchain.

References

ethereum.org
bitcoin.org