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4/8/2010

Windows Embedded CE supports two different registry types: the RAM-based registry and the hive-based registry.

Windows Mobile does not support use of the RAM-based registry.

Hive-Based Registry

The Hive-Based Registry stores registry data inside files, or hives, which can be kept on any file system. This removes the need to perform backup and restore on power off. Removing this work during start and power off makes the cold boot process faster.

Each file or hive contains a collection of registry data. The hive-based registry is split into two hives: the system hive, which contains all system data, and the user hive, which contains all data pertinent to one particular user. A multi-user system contains several user hives. A user's hive is mounted on logon and unmounted on logoff.

The hive-based registry is intended for use on devices that cold boot often, but rarely or never warm boot. It is also useful on devices that require support for multiple users.

A hive is a group of keys, subkeys, and values in the registry that has a set of supporting files containing backups of the data in the hive. A hive is treated as a single unit and is saved and restored as one file.

The system hive contains system settings that do not pertain to any one user. The OEM selects the system hive file name and location. The system hive file is typically named System.hv, but the location can vary.

The registry value SystemHiveunder HKEY_LOCAL_MACHINE\init\BootVarsindicates the path and file name of the system hive.

A user hive contains user-specific settings. All user hives are named User.hv and are located in separate user directories. Each directory is given the name of the user to whom it belongs.

The registry value ProfileDirunder HKEY_LOCAL_MACHINE\init\BootVarsindicates the location where all user directories are placed.

The boot hive contains system settings that are applied only during start. The boot hive is read out of ROM and used to start drivers and file systems needed to reach the system hive file. Once the system hive is mounted, the boot hive is discarded. Changes made to the registry during the start are copied into the system hive once it is available. The boot hive in ROM remains unchanged.

The following table shows the standard hives and their supporting files under Windows Embedded CE.

Registry hive	File	Description
Boot hive	Boot.hv, in ROM	All data under HKEY_LOCAL_MACHINE, HKEY_CLASSES_ROOT, HKEY_USERS. Used during boot only. Changes are propagated to the system hive after boot.
System hive	OEM-dependent (usually System.hv)	All data under HKEY_LOCAL_MACHINE, HKEY_CLASSES_ROOT, HKEY_USERS. Contains device-wide settings that do not vary for each user.
User hive	User.hv	All data under HKEY_CURRENT_USER. HKEY_CURRENT_USERis not located under HKEY_USERS. Contains user-specific settings. Each user has a separate hive that is mounted on logon and unmounted on logoff.

Hive-Based Registry

See Also

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