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The /install_cache option first of all executes the online search (exactly the same one as the /search option does, considering all parameters for criterias criteria and filters).
The parameter cache_dir should be a folder on a local network share where multiple machines have access to.
Before downloading the updates from the result list, WuInstall checks in the cache_dir if the update has already been downloaded there by another machine. If the update is not the cache folder, WuInstall downloads the update (from the configured download location - WSUS and/or windowsupdate.com) and puts it into the cache directory, in a subfolder, which has the same name as the Update ID.
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