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The Windows XP Embedded Enhanced Write Filter (EWF) is used to protect one
or more disk volumes by intercepting write requests to the volume and
redirecting it to an overlay volume, either RAM or another disk. Note
the EWF header conversion is only useful on Windows XP Embedded with the
Enhanced Write Filter DLL installed. It is not available on Windows XP
Pro, or other operating systems.
EWF is designed to protect the Windows boot volume so effectively it's
write protected and boots up identically each time, with any changes made
to a protected drive being lost on power down. If changes need to be
saved, EWF API calls are needed followed by a reboot to actually update
the protected drive.
Microsoft provides a command line utility EWFMGR.EXE that reports any
protected volumes and provides various commands that will be processed on
the next restart of the PC.
The EWF API allows these commands to be made from Windows applications.
The Microsoft EWFAPI.H C header file is included, with the Microsoft
help file that details the various APIs. The EWF API functions enable
applications to query and modify EWF configuration settings for protected
volumes. Typical usage scenarios for these functions include:
- Disabling/enabling EWF for a protected volume.
- Restoring or discarding an overlay level.
- Creating a checkpoint by adding an overlay level.
- Committing the current overlay.
- Persisting data through a reboot.
As well as a Delphi conversion of the EWF APIs, this package includes a
Windows demonstration application using the APIs. Please note this
program has only been testing on Windows WP Embedded running on a flash
memory C drive (IDE interface) with a single overlay in RAM. It has not
been tested with a hard disk which potentially offer multiple overlays.
1.0 - 20th October 2005 - baseline
1.1 - 5th August 2008 - updated
to be compatible with Delphi 2009
1.2 - 8th April 2009 -
added MINENUMSIZE 4 so that enumerated variables are correct length for
C++, thanks to Sven van Bruegge. This fix means the protected info
should now be correct.
A Windows demonstration application XPETEST.EXE is supplied, with source
and compiled program. When started, it displays information about any
protected drives found, and provides buttons to Disable Overlay, Enable
Overlay, Commit Overlay, Save Persistent data and Clear Command.
Compatible with Delphi 7/2006/2007/2009/2010/XE/XE2/XE3, only useful on Windows XP
Embedded with EWF installed but may be compiled or run on Windows 2000
Windows XP Embedded Enhanced Write Filter header conversion is copyright by Magenta Systems
Ltd, but may be used freely.
Magenta Systems Ltd, 9 Vincent Road,
Croydon CR0 6ED, United Kingdom
Phone 020 8656 3636, International Phone +44 20 8656 3636
Fax 020 8656 8127, International Fax +44 20 8656 8127
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