The file systems in Windows are implemented as file system drivers working above the storage system. Each of the file systems in Windows are designed to provide reliable data storage with varying features to meet the user’s requirements. A comparison of features for each of the standard file systems in Windows is shown in File System Functionality Comparison. New for Windows Server 2012 is ReFS. ReFS is a file system with scalable large volume support and the ability detect and correct data corruption on disk.

Creating a new file system driver in addition to those supplied in Windows is likely unnecessary. File Systems and File System Filter Drivers can provide any customized behavior required to modify the operation of existing file systems.

File System Filter Driver Development

A file system filter driver intercepts requests targeted at a file system or another file system filter driver. By intercepting the request before it reaches its intended target, the filter driver can extend or replace functionality provided by the original target of the request. Examples of File Systems and File System Filter Drivers include anti-virus filters, backup agents, and encryption products.

File system filtering services are available through the Filter Manager in Windows. The Filter Manager provides a framework for developing File Systems and File System Filter Drivers without having to manage all the complexities of file I/O. The Filter Manager simplifies the development of third-party filter drivers and solves many of the problems with the existing legacy filter driver model, such as the ability to control load order through an assigned altitude. A filter driver developed to the Filter Manager model is called a minifilter. Every minifilter driver has an assigned altitude, which is a unique identifier that determines where the minifilter is loaded relative to other minifilters in the I/O stack. Altitudes are allocated and managed by Microsoft.

Filter Plugfest

The Filter Plugfest is an event for file system filter driver ISVs organized by the Microsoft File System Filters team. At this event, developers work with the ISVs to solve interoperability issues among various vendor solutions and the Filter Manager.

The next Filter Plugfest has been scheduled, event details are below.


Monday, March 30, 2015 - Friday, April 3, 2015. The event begins at 9 A.M. Pacific and ends at 6 P.M. Pacific each day. Fridays end at 3:00 P.M. Pacific.


Building 92, Rooms 2320-2330. Microsoft Campus, Redmond, WA.


There is no cost for this event.

Important  Due to constraints in space and resources at this Plugfest, ISVs are required to limit their participation to a maximum of two persons representing a product to be tested for interoperability issues. There will be no exceptions to this rule, so plan for the even accordingly.


Independent Software Vendors (ISVs) and developers writing file system filter drivers and/or network filter drivers for Windows.


  • Compatibility testing with Windows 10 Technical Preview and other file systems and network filter drivers for Windows.

  • Ensuring smooth upgrade from Windows 7 and above to Windows 10 Technical Preview.


  • The opportunity to test products extensively for interoperability with other vendors' products and with Microsoft products. This has traditionally been a great way to understand interoperability scenarios and flush out any interoperability-related bugs.

  • Talks and informative sessions organized by the File System Filters & Network Filter team about topics that affect the filter driver community.

  • Opportunities to meet with file system team, network team, and cluster team at Microsoft and get answers to technical questions.

File System Filter Driver Certification

Certification information for File Systems and File System Filter Drivers is found in the Windows Hardware Certification Kit (HCK). Tests for File Systems and File System Filter Drivers are found in the Filter.Driver category of the HCK.

File System Filter Driver Developer Resources

Request an altitude allocation from Microsoft, you send an e-mail asking for an altitude assignment for your minifilter. See Minifilter Altitude Request for a description of how to submit a request.

To obtain an ID for a filter driver that uses reparse points see Reparse Point Request.

Subscribe to the NTFSD newsgroup for details about developing file systems and filter drivers. The group is found at NT File System Drivers Newsgroup.

OSR's "Developing File Systems for Windows" seminar explores developing file systems and File Systems and File System Filter Drivers. See Training for IFS Developers.



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