Bitcoin

Overview

Bitcoin is the first and largest blockchain network, launched in January 2009 by the pseudonymous Satoshi Nakamoto. It introduced the concept of a decentralized, peer-to-peer electronic cash system that operates without trusted intermediaries — no banks, no payment processors, no central authority.

The core innovation is combining cryptographic proof (Proof of Work) with economic incentives (block rewards) to create a self-sustaining network where participants are rewarded for honest behavior and penalized for dishonesty. This is described in the original Bitcoin whitepaper as solving the “double-spend problem” without a trusted third party.

Bitcoin’s monetary policy is fixed in code: 21 million coins maximum, with new supply issued through mining at a rate that halves every ~4 years. This predictable, disinflationary supply schedule is one of its most distinctive properties.

How It Works

Beginner

Bitcoin is a shared ledger that everyone can read and anyone can write to — if they follow the rules. When you send bitcoin, your transaction is broadcast to the network. Miners collect pending transactions into blocks, compete to solve a cryptographic puzzle, and the winner adds their block to the chain. Every ~10 minutes, a new block is added.

Your bitcoin isn’t stored “in” a wallet — it exists as unspent transaction outputs (UTXOs) on the blockchain. Your wallet holds the private key that proves you own those outputs.

Intermediate

Bitcoin uses the UTXO model: every transaction consumes previous unspent outputs and creates new ones. This differs from account-based systems (like Ethereum) where balances are tracked directly. UTXOs enable parallel transaction validation and provide inherent privacy benefits — each output is independent.

Transactions are signed using ECDSA (Elliptic Curve Digital Signature Algorithm) with the secp256k1 curve. Blocks are linked by including the SHA-256 hash of the previous block header, forming the chain. The Merkle tree of transactions in each block enables efficient proof that a specific transaction was included.

Builder

Block structure: version (4 bytes) + previous block hash (32 bytes) + Merkle root (32 bytes) + timestamp (4 bytes) + difficulty bits (4 bytes) + nonce (4 bytes) = 80-byte header. Max block weight: 4M weight units (SegWit). Coinbase transaction maturity: 100 blocks.

Script system: Bitcoin uses a stack-based scripting language (Bitcoin Script) that is intentionally not Turing-complete. Standard transaction types: P2PKH, P2SH, P2WPKH, P2WSH, P2TR (Taproot). Taproot (activated Nov 2021) enables Schnorr signatures and MAST for improved privacy and smart contract capability.

Consensus Mechanism

Bitcoin uses Proof of Work — miners compete to find a SHA-256 hash below a target difficulty. The difficulty adjusts every 2,016 blocks (~2 weeks) to maintain a ~10-minute block interval.

Key parameters:

• Block reward: 3.125 BTC (post-April 2024 halving)
• Next halving: ~2028
• Difficulty adjustment: Every 2,016 blocks
• Confirmation standard: 6 blocks (~1 hour) for high-value transactions

Read the full concept: Proof of Work →

Use Cases

• Store of value — “Digital gold” narrative. Fixed supply + decentralization + 15-year track record.
• Censorship-resistant payments — Permissionless transactions that no entity can block or reverse.
• Remittances — Cross-border value transfer without correspondent banking fees or delays.
• Lightning Network payments — Layer 2 enables fast, low-cost micropayments for everyday use.
• Treasury reserve — Publicly traded companies (MicroStrategy, Tesla, etc.) hold BTC on balance sheet.

Ecosystem

Wallets

• Sparrow — Desktop, privacy-focused, UTXO management
• BlueWallet — Mobile, Lightning support
• Coldcard — Hardware, air-gapped signing

Layer 2

• Lightning Network — Payment channels for instant, low-fee transactions
• Liquid Network — Federated sidechain for faster settlement and confidential transactions

Infrastructure

• Bitcoin Core — Reference node implementation
• mempool.space — Open-source block explorer and fee estimator

History & Timeline

• 2008 — Satoshi Nakamoto publishes the Bitcoin whitepaper
• 2009 — Genesis block mined (January 3). First transaction to Hal Finney.
• 2010 — First real-world transaction: 10,000 BTC for two pizzas
• 2012 — First halving: block reward drops from 50 to 25 BTC
• 2017 — SegWit activation. Bitcoin Cash fork. Price reaches ~$20K.
• 2021 — Taproot upgrade. El Salvador adopts BTC as legal tender.
• 2024 — Fourth halving: reward drops to 3.125 BTC. Spot Bitcoin ETFs approved in US.

Comparison

	Bitcoin	Litecoin	Monero
Consensus	SHA-256 PoW	Scrypt PoW	RandomX PoW
Block time	~10 min	~2.5 min	~2 min
Supply cap	21M	84M	Uncapped (tail emission)
Privacy	Pseudonymous	Pseudonymous	Private by default
Smart contracts	Limited (Script)	Limited	None
ASIC mining	Dominant	Dominant	Resistant (by design)
Primary use	Store of value	Payments	Private transactions

Related Chains

• Ethereum — Account-based model, smart contracts, PoS. The other pillar.
• Litecoin — “Silver to Bitcoin’s gold.” Scrypt PoW, faster blocks.
• Bitcoin Cash — 2017 fork. Larger blocks, payment-focused.
• Dogecoin — Merged-mining with Litecoin. Community-driven.

Learning Resources

• MIT BLC Module 1: Introduction to Blockchain (Bitcoin origin)
• MIT BLC Module 2: Maintaining Blockchain Integrity (PoW, mining, security)
• Nakamoto, S. “Bitcoin: A Peer-to-Peer Electronic Cash System” (2008) — bitcoin.org/bitcoin.pdf
• Concept pages: Proof of Work · UTXO Model · Hash Functions

Sources & Citations

1. Nakamoto, S. (2008). “Bitcoin: A Peer-to-Peer Electronic Cash System.”
2. MIT BLC Modules 1-2 (2020-2021). Blockchain and Cryptocurrency course materials.
3. Bitcoin Core documentation — bitcoincore.org
4. Halving and supply data — bitcoinblockhalf.com
5. Network statistics — mempool.space

Freshness note: Block reward and halving data current as of April 2024. Market cap rank and mining pool distribution should be verified quarterly.

Last updated: June 10, 2026