The number in your bank app is a line in a ledger
The balance in your banking app is not cash in a vault. It is one line in the bank’s ledger. Send a friend 50,000 won and the bank subtracts it from your line and adds it to theirs. Nothing moved; the ledger changed.
One bank holding the ledger is convenient. It also means money moves only when the bank allows it. Your account can be frozen, mistakes are invisible to you, and if the bank fails, everyone who trusted its ledger is shaken.
The trouble with copyable money
Could people send money over the internet without a bank? The obstacle is that digital data can be copied. A photo you send stays on your phone too. With money, that would let you send the same coin to two people at once. This is double spending.
A bank solves it by holding the ledger and deciding the order: the first payment goes through, the second bounces for lack of funds. Without a ledger keeper, who decides the order? Try it.
Press ①. One person sends the same coin to Minsu and Jieun at once. Each node keeps whichever it hears first and drops the other.
Press ① and the two payments spread in different directions; the network almost always splits — even though no node lied. There is no one to say which came first.
Press ② and one node makes a block and spreads it. The block fixes the order, every node that receives it adopts that order, and the leftover payment becomes an attempt to spend money already spent.
2008: Satoshi’s nine-page answer
On 31 October 2008 someone named Satoshi Nakamoto posted a nine-page paper to a cryptography mailing list: “Bitcoin: A Peer-to-Peer Electronic Cash System.” It promises payments from one person to another without a financial institution, and it stops double spending by giving everyone the same ordered record.
Two months later, on 3 January 2009, Bitcoin’s first block — block 0 — was created. Satoshi carved that day’s headline from The Times into it.
Where Mobick branched off
On 3 January 2019 — exactly ten years after block 0 — BTCMobick began. It inherited Bitcoin’s ledger through block #556,759 and built its own blocks from there. Splitting off from the same ledger with different rules is called a hard fork.
| Bitcoin | BTCMobick | |
|---|---|---|
| Started | 3 January 2009 | 3 January 2019 (hard fork of Bitcoin) |
| Maximum supply | 21 million BTC | 21 million BMB |
| Target block interval | ~10 minutes | ~10 minutes |
| Mining | Proof of work (SHA-256) | Proof of work (SHA-256) |
| Who mines today | Anyone (public) | The operators (private) |
The last row is the difference. Mobick is currently a private chain whose mining is run by the operators, and every newly mined coin goes to the public-goods wallets. Why, and when it plans to open up, is covered in the BTCMobick story track.
Summary
- Digital money’s first problem is double spending.
- Banks order payments by holding the ledger; Bitcoin lets blocks set the order.
- Bitcoin began on 3 January 2009; Mobick began ten years later, inheriting Bitcoin’s ledger.
Check yourself
Get them right to add a block to your chain
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Q1For money that can be copied like a file, what problem must be solved first?
Files can be copied, so the same money could be sent to two places at once. Banks solve it by keeping the ledger and setting the order; Bitcoin found a way without a bank.
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Q2In the experiment, why did the split network come back together?
Each node believes the payment it heard first, so the network splits. When a block says “this one came first” and spreads, everyone follows that order and the conflicting payment is dropped.
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Q3When did Mobick split off from Bitcoin?
Exactly ten years after Bitcoin’s block 0. 18 March 2023 was the first airdrop on Gwanaksan.
Sources
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