DBM Files

Ken Thompson developed a file organization based on hash tables that used different files for keys and the associated data records. The associated C library was named dbm.

Later on, similar libraries and file formats were developed:

ndbm
Distributed by BSD (not freely available).

sdbm
Free implementation by Ozan Yigit (1990) similar to ndbm that bases on the dynamic hash tables of P.-A. Larson. Disadvantages: Records are limited to 1kb and the implementation is slower than newer implementations.

gdbm
Free GNU implementation by Philip A. Nelson (1990) that supports data records of arbitrary lengths.

See http://www.gnu.org/software/gdbm/gdbm.html

Berkeley DB
Open-source implementation distributed by Sleepycat Software that supports B* trees, dynamic hash tables, and even transactions.

See http://www.sleepycat.com/