Request a filter altitude identifier


Microsoft will issue one "integer" altitude for each product type (by load order group). A company that already has a Microsoft-issued altitude can create its own new altitude based on its Microsoft-assigned altitude to place a new filter in the same load order group.

Microsoft will consider issuing multiple integer altitudes in the same load order group on a case-by-case basis.

Previously issued altitudes will not change.

To request a filter altitude identifier, send email in an ASCII text e-mail message to with the subject: “Filter altitude request”, and the following fields and corresponding information:

Field Comment
Company name:
Contact e-mail: Provide a long-term company email alias, versus individual email. The allocated filter altitude will be e-mailed back to this address.
Product name: Name of your filter product
Product URL: URL to your product or product's company
Product/Filter description: A one paragraph summary to help Microsoft determine an appropriate altitude for the filter.
Filter filename: Filename used for the filter
Filter type: One of these values: Registry, FileSystem, Both
Filter start-type: One of these values: Boot, System, Auto, Demand
Requested filter load order group: See Load order groups and altitudes for the list of available groups.
Requested altitude: You must request an altitude allocation in the appropriate load order group or groups for your filter. Microsoft reserves the right to assign an altitude that is different from the requested altitude, depending on altitude availability and the filter driver functionality.
Additional information: Use this field to let us know if there is any information you would like Microsoft to consider when assigning an altitude to this filter.

Example email for an altitude request

The following is an example for the body of an allocation request email.


Below is the request information to assign an altitude for our Contoso DataKleen file system minifilter.

Company name: Contoso Ltd.
Contact e-mail:
Product name: Contoso DataKleen
Product URL:
Product/Filter Description: The Contoso DataKleen filter removes all occurrences of any byte having a value between 128 and 255 during file reads. Our minifilter removes this value since it is not displayable on TTY devices.
Filter filename: ContosoDK.sys
Filter type: FileSystem
Filter start-type: Demand
Requested filter load order group: FSFilter Content Screener
Requested altitude: 268400
Additional information: None




  • All fields must be filled out. Any missing information might delay the assignment.

  • Allow Microsoft 30 business days to process and assign altitudes.

  • The assigned altitude will eventually be listed in the Allocated filter altitudes table, which is updated 1-2 times per year.