Transactions carry multiple inputs and outputs — typically several inputs combined, and at most two outputs: the payment itself and the change returned to the sender.

* Several earlier outputs fan in as inputs; the transaction fans out to two outputs — the payment and the change back to the sender. *

Handling each coin unit individually would be unwieldy, so value is split and combined through inputs/outputs. A normal transaction has either one input from a larger previous transaction or several smaller inputs merged, and usually two outputs (payment + change).

Two rules make it click: an input always spends a whole earlier output — never part of one — and whatever is left over, sum(inputs) − sum(outputs), is the miner's fee. Because your outputs almost never add up to the exact amount, the wallet sends the remainder back to you as a change output — which is why nearly every payment has two outputs.

Fan-out — a transaction depending on many earlier transactions, which depend on many more — isn't a problem: you never need to extract a complete standalone copy of a coin's entire history to spend it.

Go deeper:

• Bitcoin — Wikipedia — the transaction model, including how inputs and outputs combine value and return change.

Both restrict who can write; they differ in who can read — a public permissioned chain lets anyone read (and thus verify) the data, a private one restricts readers too.

The writer set is gated in both cases (that's what "permissioned" means). The last decision is about readers:

• Public permissioned — anyone may read the chain, so anyone can verify the validity of the stored data. Chosen when public verifiability is required.
• Private permissioned — only a limited set may read. Chosen when the participants don't need outsiders to verify the state and prefer to keep contents confidential.

Note a permissioned chain can be public even though writing is restricted — publicly verifiable content doesn't require publicly writable consensus.