What is MIME type "application/x-ms-registry"?

A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.

application/x-ms-registry is a MIME type tied to files that hold Windows registry data.
These files store the system's configuration settings in a binary format. They are critical for the OS to boot and run applications properly.

Central Config Storage: Keeps system and application settings organized.
System Boot Integrity: Provides necessary data during startup to load proper system configurations.
Backup and Recovery Usage: Serves as a backup source and is used in migrating configurations.

Files using this MIME type are often seen with formats such as DAT and HIV.
They require specialized tools like the Windows Registry Editor to view or modify the settings safely.
For further details, see Windows Registry on Wikipedia.

Associated file extensions

.dat, .hiv

Usage Examples

HTTP Header

When serving content with this MIME type, set the Content-Type header:


    Content-Type: application/x-ms-registry

HTML

In HTML, you can specify the MIME type in various elements:


    <a href="file.dat" type="application/x-ms-registry">Download file</a>

Server-side (Node.js)

Setting the Content-Type header in Node.js:


    const http = require('http');    
    
    http.createServer((req, res) => {    
      res.setHeader('Content-Type', 'application/x-ms-registry');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.dat, .hiv

FAQs

How do I open a file with the application/x-ms-registry MIME type?

You cannot open these files with a standard text editor because they are in a binary format. To view or edit them, you must use the Windows Registry Editor (regedit.exe) and use the "Load Hive" feature. Attempting to edit files like NTUSER.DAT manually can corrupt your user profile.

What is the difference between application/x-ms-registry and .reg files?

Files served as application/x-ms-registry (often .dat or .hiv) are binary system files used directly by Windows. In contrast, standard .reg files are human-readable text files used to export or import settings and usually have a text-based MIME type. See more about specific extensions like dat on our site.

How do I configure Apache to serve .hiv files correctly?

To ensure your Apache server sends the correct MIME header, add the following line to your .htaccess file or main configuration: AddType application/x-ms-registry .hiv .dat. This tells the browser strictly that the file is a Windows Registry Hive.

Is it safe to delete files identified as application/x-ms-registry?

No, deleting these files is highly dangerous and can prevent Windows from booting or users from logging in. These files, such as SYSTEM or SOFTWARE hives, contain the core configuration for the operating system. Always create a backup before managing any registry data.

Why does my browser download the file instead of displaying it?

Web browsers like Chrome, Firefox, and Edge do not have built-in rendering engines for application/x-ms-registry content. Since the browser cannot display the binary registry structure, it defaults to downloading the file to your local disk.

Can application/x-ms-registry files contain viruses?

While the file format itself is a container for settings, a malicious registry hive could alter system security settings if loaded onto a machine. Always treat unknown files with the hiv extension with caution and never load a hive from an untrusted source.

General FAQ

What is a MIME type?

A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.

MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.

MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.

How do I find the MIME type for a file?

You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.

Why are multiple MIME types listed for one extension?

Different applications and historical conventions may use alternative MIME identifiers for the same kind of file. Showing them all helps ensure compatibility across systems.