Every file system filter driver developed to the Filter Manager model (a minifilter) must have a unique identifier called an altitude. The altitude of a minifilter defines its position relative to other minifilters in the I/O stack when the minifilter is loaded. The altitude is an infinite-precision string interpreted as a decimal number. A minifilter that has a low numerical altitude is loaded below a minifilter that has a higher numerical value in the I/O stack.

Each load-order group has a defined range of altitudes. Allocation of altitudes to minifilters is managed by Microsoft.

To request an altitude for your minifilter, please click here or the Start Form button, then fill out and submit the form. An altitude will be allocated to your minifilter based on your requirements and your load-order group.

View the load-order groups and altitude ranges.

View the allocated altitudes.

Note: After an altitude is allocated to your minifilter, the company name, the filename of the minifilter, and its allocated altitude will be published here. The other information you provide will be used to contact you if there are problems or issues with the altitudes. This information will not be used for marketing purposes.

If you have any questions about the process of altitude allocation, please contact altreq@microsoft.com.

The altitude allocation request will take about 2-3 weeks time to be processed. We request you to contact altreq@microsoft.com only if you haven’t heard back from the Microsoft filter drivers team in that timeframe.

Start Form