A bit of background on the write filter- Microsoft has the UWF or Unified Write Filter available for Windows 10 IoT Enterprise thin clients (they had other write filters like EWF and FBWF for WES7, WE8S, etc previously). The write filter starts on boot (enabling or disabling prompts a reboot) and captures any and all writes to disk to an overlay called write filter cache. This cache can be in RAM (typically the case for thin clients and what we are discussing today) or on storage. So, apps think they are writing persistently to disk when in actuality, they are writing to volatile RAM and those writes are lost when unit is rebooted. Since these are typically VDI apps writing temporary data and the user generated data is in the back-end VDI infrastructure, this is actually ideal. While not entirely relevant to this discussion, I should note that the UWF does provide a mechanism to bypass itself with file, folder and registry exclusions for programs like Windows Defender, for example, that needs to frequently persist it's writes.

The write filter has two main functions:

  1. Protect the storage medium (usually eMMC or flash) from excessive writes thus extending the life of the thin client
  2. Protect the OS and user data from malware and viruses and prevent end user from filling up the disk with non-critical data like 4k videos, etc.

Typical Windows thin clients have at most 1 GB of UWF cache (some with 8 GB RAM have up to 2 GB). Once this UWF cache fills up, the OS starts complaining about low memory or low UWF cache size. Usually, once the UWF cache reaches a critical 90% level, the unit has to be rebooted. In most case, this doesn't happen for weeks, but in some deployments, this happens almost daily or more (this could be excessively verbose logging by some applications, browser cache, etc). This is an industry-wide issue for all Windows thin clietns running with the write filter enabled.

I am excited to announce the release of our brand-new patent-pending product, Overlay Optimizer that solves this very issue. Without getting into the details aka "sausage-making", I will say that Overlay Optimizer will ensure that your Windows thin client doesn't reboot as frequently as it needed to. Not only does this mean that you have a greater system up-time and therefore, a much better end-user experience; you also can avoid the need to upgrade your thin clients from say 4 GB RAM to 8 GB RAM. This patent-pending software is only available on Dell Thin Clients and will help our customers extract more performance/up-time from their thin clients. 

Overlay Optimizer is available for all Dell Thin Clients running Windows 10 IoT Enterprise and can be downloaded for free from here:


Hope this helps-please comment is this does help solve your issues.