Database engine

A database engine (or "storage engine") is the underlying software component that a database management system (DBMS) uses to create, read, update and delete (CRUD) data from adatabase. Most database management systems include their own application programming interface (API) that allows the user to interact with their underlying engine without going through the user interface of the DBMS.

The term database engine is frequently used interchangeably with database server or database management system.

Many of the modern DBMS support multiple storage engines within the same database. For example, MySQL supports InnoDB as well as MyISAM.

Some storage engines are transactional.

Name	Free	Transactional
Aria	GPL	No
BlitzDB	GPL	No
Falcon	GPL	Yes
InnoDB	GPL	Yes
MyISAM	GPL	No
InfiniDB	CPL	No
TokuDB	N/A	Yes
XtraDB	GPL	Yes

InnoDB is the default storage engine for MySQL as of MySQL 5.5. It provides the standard ACID-compliant transaction features, along with foreign key support (Declarative Referential Integrity). It is included as standard in most binaries distributed by MySQL AB, the exception being some OEMversions.

InnoDB became a product of Oracle Corporation after its acquisition of Innobase Oy in October 2005.^[1] The software is dual licensed; it is distributed under the GNU General Public License, but can also be licensed to parties wishing to combine InnoDB in proprietary software.^[2]

MyISAM was the default storage engine for the MySQL relational database management system versions prior to 5.5.^[1] It is based on the older ISAMcode but has many useful extensions. The major deficiency of MyISAM is the absence of transactions support. Versions of MySQL 5.5 and greater have switched to the InnoDB engine to ensure referential integrity constraints, and higher concurrency.

Each MyISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type. MySQL uses a .frm file to store the definition of the table, but this file is not a part of the MyISAM engine; instead it is a part of the server. The data file has a .MYD (MYData) extension. The index file has a .MYI (MYIndex) extension.

Referance: WIKI