This article is about JET Red used in. For the JET Blue implementation, see. The Microsoft Jet Database Engine (also Microsoft JET Engine or simply Jet) is a on which several products have been built. The first version of Jet was developed in 1992, consisting of three which could be used to manipulate a database. JET stands for Joint Engine Technology. And use or have used Jet as their underlying database engine. However, it has been superseded for general use, first by (MSDE), then later.

The Microsoft Jet Database Engine is a database engine on which several Microsoft products. DAO provides an API that allows programmers to access JET databases using any. 3.5, 3.51.3328.0, MSJET35. Jet 3.51 web download, 3.5+.

For larger database needs, Jet databases can be upgraded (or, in Microsoft parlance, 'up-sized') to Microsoft's flagship SQL Server database product. However, this does not mean that a MS Jet (Red) database cannot match MS SQL Server in storage capacity. A 5 billion record MS Jet (Red) database with compression and encryption turned on requires about 1 terabyte of disk storage space, comprising hundreds of (*.mdb) files, each acting as partial table, and not as a database in itself. Jet DLLs There are three modules to Jet: One is the Native Jet ISAM Driver, a (DLL) that can directly manipulate Microsoft Access database files (MDB) using (ISAM). Another one of the modules contains the ISAM Drivers, DLLs that allow access to a variety of ISAM databases, among them,, and, depending on the version of Jet.

The final module is the Data Access Objects (DAO) DLL. Provides an that allows programmers to access JET databases using any programming language.

Locking [ ] Jet allows multiple users to access the database concurrently. 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. Any single user can modify only those (that is, items in the database) to which the user has applied a, which gives exclusive access to the record until the lock is released. In Jet versions before version 4, a page locking model is used, and in Jet 4, a record locking model is employed.

Microsoft databases are organized into data 'pages', which are fixed-length (2 before Jet 4, 4 kB in Jet 4) data structures. Data is stored in 'records' of variable length that may take up less or more than one page. Flatout 2 mod cars ats. The page locking model works by locking the pages, instead of individual records, which though less resource-intensive also means that when a user locks one record, all other records on the same page are collaterally locked. As a result, no other user can access the collaterally locked records, even though no user is accessing them and there is no need for them to be locked.

In Jet 4, the record locking model eliminates collateral locks, so that every record that is not in use is available. There are two mechanisms that Microsoft uses for: pessimistic locking, and optimistic locking. With pessimistic locking, the record or page is locked immediately when the lock is requested, while with optimistic locking, the locking is delayed until the edited record is saved.

Conflicts are less likely to occur with optimistic locking, since the record is locked only for a short period of time. However, with optimistic locking one cannot be certain that the update will succeed because another user could lock the record first.