Windows Mobile 6.5 Embedded Database Engine

This article examines the database engines utilized for local application storage within Microsoft Windows Mobile 6.5. It details the primary relational engine, SQL Server Compact, as well as the underlying operating system database, EDB, clarifying how each served local data storage requirements for mobile developers.

Windows Mobile 6.5 primarily utilized Microsoft SQL Server Compact Edition (SQL CE), specifically version 3.5, as its embedded relational database engine for mobile applications. Alongside SQL CE, the operating system featured EDB (Embedded Database), a native hierarchical property database that evolved from the older CEDB engine found in earlier versions of Windows CE.

SQL Server Compact Edition (SQL CE)

SQL Server Compact 3.5 was often included directly in the ROM of Windows Mobile 6.5 devices or deployed alongside enterprise applications. It provided a lightweight, in-process relational database management system designed specifically for resource-constrained environments:

  • File-Based Storage: Databases were stored locally as single .sdf files.
  • Relational Support: It supported ANSI SQL syntax, transactions (ACID compliant), referential integrity, and indexing.
  • Synchronization: SQL CE integrated tightly with desktop and server versions of Microsoft SQL Server using Remote Data Access (RDA) and Merge Replication, making it the preferred choice for enterprise offline-sync scenarios.
  • Developer Integration: Applications built with the .NET Compact Framework accessed SQL CE using the System.Data.SqlServerCe namespace, while native C++ applications used OLE DB.

EDB (Embedded Database)

EDB was the core system-level database engine built directly into the Windows CE 5.2 kernel powering Windows Mobile 6.5. While developers could create custom EDB databases, it was predominantly used by the platform itself:

  • Operating System Store: EDB managed critical system data, including Personal Information Manager (PIM) databases such as Contacts, Appointments, and Tasks.
  • Improvements over CEDB: EDB replaced the legacy CEDB engine, introducing support for transactions, multiple sort orders per table, and database file encryption.
  • Access: Developers accessed EDB through native Win32 APIs, primarily via the CeMountDBVolEx and related Ce* database functions.

For custom third-party applications requiring relational data structures and SQL querying on Windows Mobile 6.5, SQL Server Compact 3.5 served as the standard embedded storage engine.