MS Access can also use Paradox files using its own library. Paradox files can store numbers and other types of data more efficiently than DBF files. Usually Paradox files are keyed, which means that there is a field or set of fields with a unique value. This keying speeds up many operations. The primary index is stored in two separate files and each secondary index is stored as two additional files.
Indexes can be on multiple fields.
Paradox version 4 and higher allow validation rules to be places on the data. Record locking for all tables in the system is achieved through a single file. This can really speed up record locking operations for multiple users accessing multiple tables. The downside is that every user must have their engine set up correctly or the data tables will be corrupted. Many users and even database administrators are unaware of how important this configuration is and thus it is quite common to not be configured correctly.