Bitcoin & Base-Layer Fundamentals

How Bitcoin actually works: blocks, transactions, halvings, SegWit, Taproot, and the protocol rules that make it tick.

• What Is Bitcoin?

  Bitcoin is a decentralized digital currency that allows peer-to-peer transactions without banks or intermediaries. It runs on a public ledger called a blockchain, secured by cryptographic proof-of-work mining, with a hard supply cap of 21 million coins.

• What Is Proof of Work?

  Proof of work is a consensus mechanism where miners expend computational energy to solve a cryptographic puzzle, proving they did real work before they can add a new block to the blockchain. It prevents spam and double-spending without a central authority.

• What Is a Bitcoin Halving?

  A Bitcoin halving is a programmed event that cuts the block reward miners receive in half every 210,000 blocks (roughly every four years). It enforces Bitcoin's disinflationary supply schedule, reducing the rate of new coin creation until the 21 million cap is reached.

• What Is the Bitcoin Block Reward?

  The block reward is the newly minted Bitcoin a miner receives for successfully adding a valid block to the blockchain. It currently stands at 3.125 BTC per block (since April 2024) and is the primary mechanism through which new Bitcoin enters circulation.

• What Is a Bitcoin Block?

  A Bitcoin block is a batch of verified transactions bundled together and added to the blockchain approximately every 10 minutes. Each block contains a header (with the previous block's hash, a timestamp, and a nonce) and a body (the transactions themselves), forming a tamper-evident chain.

• What Is a UTXO (Unspent Transaction Output)?

  A UTXO is an unspent transaction output, a discrete chunk of Bitcoin that has been received but not yet spent. Bitcoin doesn't use account balances; instead, your "balance" is the sum of all UTXOs your private key can spend, like having specific bills in a wallet rather than a bank balance.

• What Is Bitcoin's 21 Million Supply Cap?

  Bitcoin's code enforces a hard cap of 21 million coins that can ever exist. This limit is achieved through the halving schedule, cutting the block reward in half every 210,000 blocks, creating a geometric series that converges on 21 million by approximately 2140.

• What Is a Bitcoin Address?

  A Bitcoin address is a short alphanumeric string (26-62 characters) derived from your public key that serves as a destination for receiving Bitcoin. It is not your public key itself, it is a hashed, encoded version with a built-in checksum to prevent typos.

• What Are Bitcoin Transaction Confirmations?

  A confirmation is each new block added to the blockchain after the block containing your transaction. One confirmation means your transaction is in the latest block; six confirmations (the common security threshold) means five additional blocks have been mined on top of it, making reversal computationally impractical.

• What Is SegWit?

  SegWit (Segregated Witness) is a Bitcoin protocol upgrade activated in August 2017 that separates transaction signature data (the "witness") from the main transaction body. This fixes transaction malleability, enables Layer 2 solutions like Lightning, and effectively increases block capacity without changing the block size limit.

• What Is Taproot?

  Taproot is a Bitcoin upgrade (activated November 2021) that uses Schnorr signatures and MAST (Merkelized Alternative Script Trees) to make complex transactions look identical to simple ones on-chain. It improves privacy, reduces fees for multi-signature and smart contract transactions, and enables more expressive scripting.

• What Is a Bitcoin Full Node vs. a Light Client?

  A full node downloads and validates the entire blockchain (500+ GB), independently verifying every transaction and block against consensus rules. A light client (SPV client) only downloads block headers and trusts full nodes to confirm transaction inclusion, faster and lighter but less trustless.

• What Is the Bitcoin Mempool?

  The mempool (memory pool) is each Bitcoin node's waiting room for unconfirmed transactions. When you broadcast a transaction, it sits in mempools across the network until a miner includes it in a block. Miners typically select transactions with the highest fee rates first.

• What Is a Bitcoin Difficulty Adjustment?

  The difficulty adjustment is Bitcoin's self-regulating mechanism that recalibrates the mining difficulty every 2,016 blocks (~2 weeks) to keep the average block time at approximately 10 minutes, regardless of how much total hash power is on the network.

• What Is a Coinbase Transaction?

  A coinbase transaction is the first transaction in every Bitcoin block, the one that creates new coins out of nothing and pays the miner their block reward. It has no inputs (no coins being spent); it creates outputs from the protocol's emission schedule plus collected transaction fees.

• What Is Bitcoin Script?

  Bitcoin Script is a simple, stack-based programming language used to define the conditions under which Bitcoin can be spent. It is intentionally not Turing-complete, it cannot loop, which makes it predictable, auditable, and prevents denial-of-service attacks on the network.