Don’t just trust. Verify.
Bitcoin is a digital asset you can send and receive over the internet, measured in BTC. Instead of relying on one bank or organization to keep the transaction record, participants check it against shared rules. Its exchange price changes, and it is not legal tender in Japan.
Check the six reference facts and evidenceFree to read. No ads, no sign-up, and nothing here to buy or sell.
A small window into cryptography.
Change B to b: 62 of 64 hexadecimal digits change. Underlines mark differences from Bitcoin.
Two precomputed examples of single SHA-256, not a mining simulation. Try your own text in the lab.
Open the verification labThe big-picture path · about 33 min
Verification lab
One changed character, a different hash, a broken reference. Experiment in your browser, then discover why a chain of hashes alone is not Bitcoin.
Try it yourselfChange the record. Does the next block notice?
An educational model. No transactions or mining.
This comparison covers Japanese yen and typical yen-denominated prepaid e-money in Japan. Not every payment app works in the same way.
For example, you could keep exactly 0.001 BTC while its value in yen changes. A BTC balance is not the same as a balance denominated in yen.
Check the yen price and its retrieval timeYou can send BTC to a willing recipient without routing it through a bank account. On-chain fees and confirmation times vary; payments are not always cheap or fast.
Understand payments and feesYou can manage your own keys or entrust custody to a provider. The risks differ: losing keys and recovery methods in the first case, and service failures or insolvency in the second.
Compare custody choicesBitcoin is also traded, but neither your principal nor a higher price is guaranteed. Be wary of guaranteed-profit pitches and anyone asking for private keys or recovery phrases.
Recognize scams and warning signsThere is no central help desk that can cancel a well-confirmed payment like a bank recall. Check the destination, amount, and network before sending.
Next, read how transactions are checkedStart with three views of the same system: currency, network, and ledger.
Cryptoassets are a broad category, and Bitcoin (ビットコイン) is one of them. Bitcoin has no single company or central server that maintains its balance ledger. A holder authorizes a payment with a private-key signature and relays the transaction across a peer-to-peer network. BTC is the unit used to state amounts within that system.
Miners propose blocks backed by proof of work. Full nodes independently check each transaction and block against consensus rules. The system converges on the valid chain with the most cumulative work; it is not a vote that can make an invalid block valid.
The issuance limit is commonly described as roughly 21 million BTC, with the subsidy halving every 210,000 blocks. That is a rule checked by nodes, not a law of nature or a guarantee of a higher price. Because transaction history is public, Bitcoin is pseudonymous rather than anonymous.
This library does not isolate Bitcoin from its foundations. It connects computing history from EDVAC through CPUs, GPUs, FPGAs, and ASICs, distributed systems, SETI@home and BOINC, PrimeGrid, World Community Grid, consensus, blockchain design, economics, institutions, and criticism in one source-linked map.
Claim, boundary, evidence
This page is an editorial synthesis of original records. It does not pretend to be the historical or protocol primary source; every claim leads back to the paper, archive, code, or official project record that supports it.
Depending on context, Bitcoin can mean the protocol, the running network, or the digital asset. BTC is the widely used unit label for amounts.
The boundary
Bitcoin and blockchain are not synonyms. Bitcoin combines signatures, peer-to-peer relay, consensus rules, proof of work, and incentives.
The whitepaper announcement under the name Satoshi Nakamoto is dated October 31, 2008; the genesis block January 3, 2009; and the Bitcoin v0.1 release announcement January 8, 2009.
The boundary
The paper, the first block, and the public software announcement are different events. Any Bitcoin start date should say which milestone it uses.
Miners propose blocks backed by proof of work, while full nodes independently check blocks and transactions against consensus rules. Selection is among valid chains, choosing the one with the most cumulative work.
The boundary
A majority of hash rate is not permission to spend without a private key or unilaterally create out-of-rule BTC that validating nodes reject.
Under the consensus rule visible in Bitcoin Core v30.0, the block subsidy starts at 50 BTC and is halved every 210,000 blocks by an integer right shift. Applying that rule to completion yields a theoretical maximum of 20,999,999.9769 BTC.
The boundary
The cap is a consensus rule, not a law of nature. It is not mathematically impossible to alter; doing so would require an incompatible rule change and adoption, which makes it exceptionally difficult.
Bitcoin transaction history is public. Addresses do not contain real names by default, so the system is pseudonymous, but related activity can become traceable when an address is linked to a person or service.
The boundary
Using fresh addresses can reduce linkability but does not guarantee anonymity; transaction graphs, amounts, timing, and service records can provide clues.
No single organization owns Bitcoin as a whole. Bitcoin Core contributors propose and publish software, while node operators, miners, wallets, exchanges, and users decide what they adopt and run.
The boundary
The absence of one central operator does not mean every surrounding layer is evenly distributed. Mining pools, ASIC manufacturing, exchanges, and custody can be concentrated.
Evidence last checked: . Please report errors or stale evidence through the corrections contact. Corrections contact
Follow every core claim back to the whitepaper, early correspondence, Bitcoin Core, BIPs, and public records, then place it within 45 topics spanning computing history, distributed systems, and blockchain.
The library currently holds 45 articles and 19 BIP summaries, backed by 452 cited sources and 42 diagrams.
From EDVAC and the transistor through Cell/B.E., CPUs, GPUs, FPGAs, and ASICs: a primary-source history of the PS3 Folding@home client, BOINC, Bitcoin mining, the companies, and the supply chain.
From ENIAC, CDC 6600, Cray-1, the Earth Simulator, Fugaku, and exascale to AI-HPC integration, hybrid quantum computing, and evidence-bounded scenarios for 2031 and 2036.
How CPU latency, GPU throughput, RAM, VRAM, HBM, training state, inference, and the KV cache shape AI computers, and where computing goes next.
A primary-source guide to qubits, Shor and Grover, error correction, Bitcoin signatures and SHA-256, public-key exposure, and draft BIP 360.
Five- and ten-year computing scenarios with labeled confidence, why AI capability is task-specific while responsibility stays human, and what blockchain, identity, payments, and audit can and cannot do for AI agents.
From ARPANET to logical clocks, Byzantine faults, FLP, CAP, and replicated state machines: the foundations that long predate blockchain.
From GIMPS, SETI@home, and BOINC through PS3 Cell/Folding@home and NTT DATA cell computing Gene: how spare computing capacity became research infrastructure and managed grids.
From BOINC points and team competition to Bitcoin and Ethereum rewards, AI demand, and computing in space: a primary-source account of who directed CPUs, GPUs, and electricity, and why.
How WCG works, from its 2004 launch at IBM and its transfer to the Krembil Research Institute to BOINC work distribution, validation, medical and climate research, published results, and how it runs today.
Compare distributed consensus by membership, fault model, synchrony, quorums, Sybil resistance, and finality, from Paxos and Raft to PBFT and Bitcoin.
A primary-source guide that treats blockchain as a design space, combining membership, data models, consensus, finality, execution, data availability, oracles, and governance, rather than as one monolithic technology.
Bitcoin Library (bitcoin.ne.jp) is a free educational site operated by KK siiiiiixth, connecting Bitcoin to computing history, distributed systems, the social history of compute, and blockchain foundations. It is not a public-library catalog service. Learn more on the About Bitcoin Library page, and see how we write on the editorial policy page.