Why does Explorer read files when I just browse the directory?

Explorer tries to obtain icons from the file resources. That's why it performs the reading of files during directory enumeration. It isn't necessary to read a whole file but only the part that Explorer requests. Also it's possible to decrease the quantity of information being read. To do this, use the network type of mounting point. In this case, Explorer minimizes the amount of requested information. Another option is to report files to have the Offline attribute (FILE_ATTRIBUTE_OFFLINE). Explorer doesn't read thumbnails for offline files. However, the attribute is visible to the user (Explorer displays an overlay image for offline files) so you might want not to use the attribute.

Also, to further increase productivity, you can start caching such information asynchronously at the time when Explorer opens the directory and uses the already cached information in subsequent OnReadFile requests.

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