dash/doc/files.md

• bitcoin.conf: contains configuration settings for bitcoind or bitcoin-qt
• bitcoind.pid: stores the process id of bitcoind while running
• blocks/blk000??.dat: block data (custom, 128 MiB per file); since 0.8.0
• blocks/rev000??.dat; block undo data (custom); since 0.8.0 (format changed since pre-0.8)
• blocks/index/*; block index (LevelDB); since 0.8.0
• chainstate/*; block chain state database (LevelDB); since 0.8.0
• database/*: BDB database environment; only used for wallet since 0.8.0
• db.log: wallet database log file
• debug.log: contains debug information and general logging generated by bitcoind or bitcoin-qt
• fee_estimates.dat: stores statistics used to estimate minimum transaction fees and priorities required for confirmation; since 0.10.0
• peers.dat: peer IP address database (custom format); since 0.7.0
• wallet.dat: personal wallet (BDB) with keys and transactions

Only used in pre-0.8.0

• blktree/; block chain index (LevelDB); since pre-0.8, replaced by blocks/index/ in 0.8.0
• coins/; unspent transaction output database (LevelDB); since pre-0.8, replaced by chainstate/ in 0.8.0

Only used before 0.8.0

• blkindex.dat: block chain index database (BDB); replaced by {chainstate/,blocks/index/,blocks/rev000??.dat} in 0.8.0
• blk000?.dat: block data (custom, 2 GiB per file); replaced by blocks/blk000??.dat in 0.8.0

Only used before 0.7.0

• addr.dat: peer IP address database (BDB); replaced by peers.dat in 0.7.0