Persistent Storage

As mentioned earlier, the storage memory portion of RAM is referred to as the object store. It includes three types of data storage:

• The Windows CE file system, which contains application and data files.
• The Windows CE database, which provides structured storage. It offers an alternative to storing user data and application data in files or in the registry.
• The Windows CE system registry, which is used to store the system configuration and any other information that an application must access quickly.

The Windows CE file system holds executable files and data files that the user installs or creates. It supports up to nine FAT volumes. Each volume is treated as a storage card. If a storage card has multiple partitions, then each partition is treated as a separate volume. It is possible to support other types of file systems by writing block device drivers. For more information on block device drivers, see the documentation for the Windows CE Device Driver Kit (DDK). Files are typically stored in compressed form. Applications access the file system with standard Win32 file system functions. For more information about file management, see Accessing Persistent Storage.

To reduce the data loss during a critical failure, such as loss of power, the Windows CE file system is transactioned. In addition, the file system implements a transactioned mirroring scheme to track FAT file system operations that are not transactioned. The mirroring scheme restores the FAT volume if power is lost while a critical operation is performed.

The Windows CE database provides general-purpose, structured storage of data, but it is not a full-fledged database. In particular, Windows CE databases have only one level of hierarchy. Records cannot contain other records, nor can they be shared between databases. For more information about storage, see Accessing Persistent Storage.

Platforms that implement the Windows CE operating system commonly ship with one or more built-in databases. For example, the H/PC comes with calendar and contacts applications that use databases to store their information. Windows CE provides an API that allows users and applications to create and use additional databases as needed.

The system registry is used to store a variety of information, such as system or application configuration data. It is similar to the registry found on Windows-based desktop platforms. Applications running on a Windows CE-based device can access and modify information in the registry with standard Win32 functions.

It is also possible to access the Windows CE object store from an attached desktop computer using one of the following approaches:

• The Windows CE Remote API (RAPI) includes a set of functions that you can use to manipulate the file system and the registry. An application running on the desktop computer invokes RAPI functions, which act on the object store of the linked Windows CE-based device. For more information, see Invoking Functions from a Desktop Computer.
• Windows CE offers an extensive and sophisticated set of tools for transferring data between a desktop computer and an attached Windows CE-based device. For example, you can use these tools to synchronize data between a Windows CE-based device and an attached desktop computer when you update a list of contacts. For more information, see Synchronizing Data.
• The object store can also be modified when installing an application. For more information, see Installing and Managing Applications.