UTXO — a ledger with no balance column

No balance column

A bank ledger has a balance per account and edits it. Bitcoin’s and Mobick’s ledgers do not. Nowhere does it say “this address: 5 BMB.”

Instead the ledger holds outputs left by transactions. An output says “this amount can be spent by whoever holds this address’s key.” Outputs nobody has spent yet are UTXOs (unspent transaction outputs). Your wallet’s balance is just the sum of the UTXOs at your addresses.

Think of banknotes. 50,000 won might be five 10,000 notes or one 50,000 note. UTXOs, like notes, exist one by one.

Paying with coins and getting change

You cannot tear a banknote in half, and you cannot split a UTXO. To send 2 BMB when all you have is a 3.125 BMB UTXO, you spend all of it and get change. Try it.

Amount to send

0.7 BMB2 BMB4 BMB

Fee (example)0.0001 BMB

My UTXOs — tap to pick

Balance = sum of the coins 0

Transaction

Inputs

0

Send

0

Fee

0.0001

Change

—

Sign and send Reset

New outputs

After sending you will see three things:

• The coins you used are spent and gone — never usable again. Spending the same coin twice is rejected instantly by nodes.
• A payment output and a change output are created; change comes back to your own address.
• The fee appears nowhere as an output. Inputs − outputs is the fee, and the miner who includes the transaction keeps it.

What a transaction looks like

Now you can say it in one sentence: a transaction consumes some UTXOs and creates new ones.

• Inputs: which UTXOs (the transaction ID and output number that created them), plus a signature proving you own them.
• Outputs: how much, locked to which address’s key.

The signatures from the previous lesson live in the inputs. Nodes check each input — is this UTXO still unspent? does the signature match its address? — and drop the whole transaction if anything fails.

UTXOs on the Mobick chain

Right now the Mobick mainnet holds 465,628 unspent outputs. Every BMB sits in one of them, and together they make up the 19,885,668.75 BMB issued so far.

UTXOs existing one by one has mattered twice for Mobick, and will again:

• The New Bedford upgrade (17 February 2026): moving the whole ledger to a new chain, Mobick did not copy balances; it verified and moved 382,060 UTXOs one by one — 235,230 addresses, 3,879,641.131 BMB.
• Whale hunting (planned): take a snapshot of Bitcoin’s UTXOs at some moment and let their owners claim Mobick by signing with their keys. UTXOs that are claimed are alive; those that never move can be treated as lost — a way to reveal how many of Bitcoin’s 21 million are really still owned.

Summary

• The ledger has no balance column; a balance is the sum of your UTXOs.
• UTXOs cannot be split. You spend them whole and get change as a new output.
• Fee = inputs − outputs, taken by the miner.
• At New Bedford, Mobick moved 382,060 UTXOs to the new chain one by one.