Data is stored in 'records' of variable length that may take up less or more than one page.

Microsoft databases are organized into data 'pages', which are fixed-length (2 kB before Jet 4, 4 kB in Jet 4) data structures. In Jet versions before version 4, a page locking model is used, and in Jet 4, a record locking model is employed. Any single user can modify only those database records (that is, items in the database) to which the user has applied a lock, which gives exclusive access to the record until the lock is released. To prevent that data from being corrupted or invalidated when multiple users try to edit the same record or page of the database, Jet employs a locking policy. Jet allows multiple users to access the database concurrently.

DAO provides an API that allows programmers to access JET databases using any programming language. The final module is the Data Access Objects (DAO) DLL. Another one of the modules contains the ISAM Drivers, DLLs that allow access to a variety of Indexed Sequential Access Method ISAM databases, among them xBase, Paradox, Btrieve and FoxPro, depending on the version of Jet. There are three modules to Jet: One is the Native Jet ISAM Driver, a dynamic link library (DLL) that can directly manipulate Microsoft Access database files (MDB) using a (random access) file system API. It comprises typically hundreds of *.mdb files.

For larger database needs, Jet databases can be upgraded (or, in Microsoft parlance, 'up-sized') to Microsoft's flagship SQL Server database product.Ī five billion record MS Jet (Red) database with compression and encryption turned on requires about one terabyte of disk storage space. However, it has been superseded for general use, first by Microsoft Desktop Engine (MSDE), then later by SQL Server Express. Microsoft Access and Visual Basic use or have used Jet as their underlying database engine. The first version of Jet was developed in 1992, consisting of three modules which could be used to manipulate a database. The Access Database Engine (also Office Access Connectivity Engine or ACE and formerly Microsoft Jet Database Engine, Microsoft JET Engine or simply Jet) is a database engine on which several Microsoft products have been built.

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