KEB C6 E22 BM-RVL, Инструкция по эксплуатации

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OPErATING SySTEMS
4.2 KEB Write filter Manager (KEB-Wf_MGr)
4.2.1 Introduction
KEB Write Filter Manager bases on the Enhanced Write Filter (EWF) from Microsoft for
Windows Embededd Standard 7(WES7).
4.2.2 How EWf works
EWF protects a volume from write access. This is realized by an EWF Overlay: EWF
protects the contents of a volume by redirecting all write operations to another storage
location. This location is called an overlay. An EWF overlay can be in RAM, or on ano-
ther disk partition. An overlay is conceptually similar to a transparency overlay on an
overhead projector. Any change that is made to the overlay affects the picture as it is
seen in the aggregate, but if the overlay is removed, the underlying picture remains
unchanged.
When EWF is enabled for a volume, every write operation to that volume will be redirec-
ted to an overlay in RAM and no data will be persistently stored into the volume. In case
of a reboot or of a system restart after a power failure the overlay will be reset and all the
data written in the previous session will be lost. The view of the volume will be the same,
after every reboot. Thus the content of the volume is protected by any damage which
can be caused by power fails otherwise.
4.2.3 Protectable Volumes
Volume Protecable Intention
C:\ Yes olds the operating system (including the registry) and the
installed programs. Should be protected to ensure that the
system never becomes unbootable.
D:\DATA No For free data storage, future use
E:\CfAST Yes Holds the Control and HMI applications. Should be protec-
ted to ensure that the applications never become invalid.
4.2.4 KEB EWF configuration
On KEB devices RAM overlay is used and the EWF configuration is stored in the registry
of the WES7 operating system, which resides with the operating system on volume C:\.
This implies that changes to the EWF configuration are only possible if the EWF for volu -
me C:\ is disabled or the changes to C:\ will be committed. Otherwise they will be discar-
ded after a reboot. The following table shows the dependencies between the volumes: