nonSegWit

NonSegWit refers to Bitcoin transactions that do not utilize Segregated Witness (SegWit). SegWit, activated in 2017, introduces a separate witness data structure for signatures and moves it out of the main transaction block, allowing more efficient use of block space and enabling fixes for transaction malleability. NonSegWit transactions use the legacy transaction format and do not include a witness field. They are serialized without the SegWit marker and flag, and they typically spend from inputs such as P2PKH or P2SH.

In this mode, the transaction ID (txid) is the double SHA-256 hash of the serialized transaction. Because there is no witness data, there is no separate witness-based wtxid for nonSegWit transactions; the txid fully identifies the transaction. The outputs and scripts can still allocate to legacy or SegWit-enabled addresses, but the spending path on nonSegWit transactions remains the traditional scriptSig-based validation.

From a network and fee perspective, SegWit transactions generally achieve lower fees per unit of block space due to witness data discounting in the block weight metric. NonSegWit transactions can be less efficient in high-traffic periods and may require higher fees to achieve timely confirmation. Despite the rise of SegWit, nonSegWit remains supported for backward compatibility, ensuring compatibility with older wallets and services that have not migrated to SegWit.