What is Bitcoin (BTC)?

The first and largest cryptocurrency, launched in 2009 as a peer-to-peer digital cash system with a fixed supply of 21 million coins.

Bitcoin runs on its own blockchain and is available on nearly every exchange. It is the asset most jurisdictions have regulated first, the one with the deepest order books, and the default listing for any venue that lists anything at all.

The thing newcomers get wrong is the unit. You do not need to buy a whole coin. Bitcoin divides to eight decimal places, and the smallest unit is a satoshi, so a $20 purchase is an ordinary transaction rather than a rounding problem.

How it works

Transactions are collected into blocks by miners competing to find a valid proof of work solution. The network targets one block roughly every ten minutes and adjusts difficulty every 2,016 blocks to hold that pace as hardware changes.

New coins enter through the block subsidy. Bitcoin Core's consensus code starts the subsidy at 50 coins and halves it every 210,000 blocks, forcing it to zero after 64 halvings (source: Bitcoin Core, GetBlockSubsidy in validation.cpp). That schedule is what produces the 21 million limit.

Balances are tracked as unspent transaction outputs rather than account balances. A transaction consumes whole outputs and creates new ones, which is why wallets produce change outputs and why coin control exists.

Upgrades happen through Bitcoin Improvement Proposals and require broad agreement, which is why Bitcoin changes slowly compared with other chains. Segregated Witness and Taproot are the two most consequential recent ones.

Confirmations are probabilistic rather than final. Each additional block on top of yours makes reversal exponentially more expensive, which is why exchanges wait a set number of blocks before crediting a deposit.

Example

Illustrative: you buy $200 of Bitcoin at $60,000 per coin. That is 0.00333 BTC, or 333,000 satoshis. You withdraw it to your own wallet and pay a network fee quoted in sat vb, say 8 sat per virtual byte on a 141-byte transaction, which is about 1,128 satoshis, or roughly $0.68. The exchange may charge its own withdrawal fee on top. Figures are illustrative; fee rates change with demand for block space.

Why it matters when you buy

Bitcoin is where availability, spreads, and regulatory clarity are best, which makes it the reference point for judging everything else. If an asset is thinner, more expensive to trade, or unavailable where you live, Bitcoin is the comparison that shows by how much. See what venues serve you at the exchange directory, compare costs at the fee comparison, and see the Bitcoin asset page.

Related terms

• satoshi — the smallest unit, one hundred millionth of a coin
• bitcoin halving — the scheduled cut to new issuance
• proof of work — the consensus mechanism securing it
• utxo — how balances are actually represented
• confirmation — how settlement certainty accumulates
• block subsidy — the source of new coins

Questions

Do I have to buy a whole bitcoin?

No. It divides to eight decimal places, so any amount above a venue's minimum order size works. Most exchanges set that minimum in the low single digits of dollars.

Why do withdrawals sometimes take an hour?

Because exchanges wait for a set number of confirmations before releasing funds, and each confirmation is a new block averaging about ten minutes. Congested periods add waiting time in the mempool as well.

Is Bitcoin anonymous?

No. Every transaction is public and permanent, and analytics firms link addresses to identities routinely. It is pseudonymous at best, and exchange deposits tie an address to your verified identity.