Mastering Blockchain - Second Edition

Inputs

Generally, each input spends a previous output. Each output is considered as Unspent Transaction Output (UTXO) until an input consumes it. UTXO is an unspent transaction output that can be spent as an input to a new transaction.

Transaction input data structure is shown in the following table:

Field	Size	Description
Transaction hash	32 bytes	This is the hash of the previous transaction with UTXO.
Output index	4 bytes	This is the previous transactions output index, that is, UTXO to be spent.
Script length	1-9 bytes	This is the size of the unlocking script.
Unlocking script	Variable	Input script (ScriptSig) which satisfies the requirements of the locking script.
Sequence number	4 bytes