Block

Block is the fundamental record-keeping unit of Bitcoin: a bundle of confirmed transactions, sealed by a cryptographic header, that miners compete to add to the end of the blockchain roughly every ten minutes.

Also known as: a Bitcoin block, or simply “a block” on the chain.

What a block actually contains

Every block has two parts: a body holding the transactions, and an 80-byte block header that summarises and seals them. The header is assembled from six fields in a fixed order — the protocol version, the hash of the previous block, the merkle root (a single fingerprint of every transaction in the block), the timestamp, the compact difficulty target (nBits), and finally the nonce. The first transaction in the body is always the coinbase transaction, which pays the miner the newly minted coins plus accumulated fees.

Because the previous block’s hash is baked into every new header, blocks form an unbroken chain. Change one transaction in an old block and its merkle root changes, which changes that block’s hash, which breaks the link in every block that came after it. That chaining is what makes Bitcoin’s history practically impossible to rewrite without redoing all the work.

How a block gets mined

Mining a block is a search problem. Your hardware repeatedly hashes the 80-byte header with double SHA-256, tweaking the nonce (and version bits, via ASICBoost) on each attempt, looking for an output below the network target. The lower the target, the higher the difficulty, and the more hashes the whole network must grind through on average to find a valid block. Bitcoin retargets that difficulty on a fixed schedule so that blocks keep arriving at roughly the intended cadence regardless of how much hashrate joins or leaves.

The work miners send their ASIC chips is just a block template handed down by a pool over the stratum protocol: previous-block hash, coinbase pieces, merkle branches, ntime, nBits, and version. The chip builds the header, hashes it, and reports any nonce that clears the bar. When a header finally hashes below the full network target, that header — plus its body — is a freshly mined block, broadcast to every node on Earth.

Why a home or ASIC miner cares

For most plebs, finding a whole block alone is a long-odds event — which is exactly why mining pools exist. A pool sets an easy share target, your miner submits shares as proof it is genuinely working, and when any member of the pool actually lands a block, the block reward is split according to the pool’s accounting rules. Whether you join a pool or chase the jackpot via solo mining on a small rig, the chip-level job is identical: hash headers, beat a target, hope to seal a block.

This is where firmware and tuning matter to your bottom line. Squeezing more valid header hashes per joule — through careful undervolting, per-domain voltage tuning, and frequency tuning whose values are calculated at runtime rather than fixed presets — raises your share of the network’s block-finding lottery without raising your power bill. That is the whole game of running efficient hardware, and it is one more layer of the network kept decentralised every time an independent miner, rather than a single large facility, seals the next block. If you want to compare tuning stacks, our firmware comparison lays out the trade-offs, and our Bitaxe hub covers open hardware small enough to run a real solo block lottery from a desk.

Related terms: Block reward, Block header, Coinbase transaction, Proof of work, Halving, Solo block

From chip term to open-source miners

Connect the chip definition to setup guides, troubleshooting, miner specs, and commercial open-source mining hardware.

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• Bitaxe troubleshooting guide
• Bitaxe Gamma specs
• BM1366AL ASIC chip
• Open-source miners and accessories