`blocks/` | `revNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Block undo data (custom format)
`chainstate/` | LevelDB database | Blockchain state (a compact representation of all currently unspent transaction outputs and some metadata about the transactions they are from)
`indexes/txindex/` | LevelDB database | Transaction index; *optional*, used if `-txindex=1`
`indexes/blockfilter/basic/db/` | LevelDB database | Blockfilter index LevelDB database for the basic filtertype; *optional*, used if `-blockfilterindex=basic`
`indexes/blockfilter/basic/` | `fltrNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Blockfilter index filters for the basic filtertype; *optional*, used if `-blockfilterindex=basic`
`wallets/` | | [Contains wallets](#multi-wallet-environment); can be specified by `-walletdir` option; if `wallets/` subdirectory does not exist, a wallet resides in the data directory
`./` | `banlist.dat` | Stores the IPs/subnets of banned nodes
`./` | `bitcoin.conf` | Contains [configuration settings](bitcoin-conf.md) for `bitcoind` or `bitcoin-qt`; can be specified by `-conf` option