SBC-GX1 Windows XP Embedded Quickstart Enhanced Write Filter
Enhanced Write Filter
RAM-based Enhanced Write Filter (EWF) allows you to protect the operating system so
that any writes to the CompactFlash are not permanent. Instead, they are redirected to
an overlay in memory so that whilst the operating system is running they appear
permanent, but when it is shutdown or rebooted the writes are lost and the operating
system reverts to the same state it was in at the previous boot. If you decide that the
changes written to the overlay should be kept, a utility can be run and the changes are
committed during the next shutdown.
The Standard XPe and Minimal XPe images are supplied with RAM-based EWF
functionality included but disabled. The management utility ewfmgr.exe can be used to
control the status of EWF. Several batch files are included on the Start menu. These
files use the utility with the correct parameters to allow the status of EWF to be changed
very simply.
When the status of the EWF is changed, the update does not happen immediately. The
changes take effect as the operating system is shut down. If you use the Start menu
shortcuts to change the status of EWF, you are prompted to restart the machine.
An API is included which allows the user to query and control the status of EWF from
within their application. Full details of the functions and structures, along with some
sample code, can be found at www.msdn.microsoft.com/library/en-
us/xpehelp/html/xetbsEnhancedWriteFilterAPI.asp.
© 2004 Arcom Issue D 27
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