What is MIME type "text/x-asm"?

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

The MIME type text/x-asm denotes plain text files that contain assembly language source code. These files list low-level instructions directly processed by a computer's CPU after they are assembled into machine code.

Assembly language is used in system programming and embedded systems. It offers fine-grained control over hardware and performance-critical tasks.

Assembly language development – Writing and editing low-level code.
System programming – Creating and adjusting OS kernels or drivers.
Embedded systems – Programming devices where hardware control is critical.

Files using this MIME type are typically stored with the extensions S and ASM.

This type is common in development environments that support syntax highlighting in text editors. The plain text format makes it easy to read and modify using simple tools or more advanced integrated development environments.

Associated file extensions

.s, .asm

Usage Examples

HTTP Header

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


    Content-Type: text/x-asm

HTML

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


    <a href="file.dat" type="text/x-asm">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', 'text/x-asm');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.s, .asm

FAQs

How do I open a file with the text/x-asm MIME type?

Because text/x-asm files are plain text, you can view and edit them in any standard text editor like Notepad, Vim, or VS Code. For the best experience, use an editor that supports syntax highlighting for Assembly language to make the code structure easier to read.

How do I configure Apache to serve .asm and .s files correctly?

You can map these extensions to the correct MIME type by modifying your .htaccess or server configuration file. Add the line AddType text/x-asm .asm .s to ensure Apache sends the correct Content-Type header to browsers and clients.

Why does my browser download text/x-asm files instead of displaying them?

Most web browsers do not have built-in rendering logic for the text/x-asm type, so they default to downloading the file. To force the browser to display the code inline, you can set the Content-Disposition: inline header on the server or serve the file as text/plain.

Is text/x-asm a standard IANA MIME type?

No, the x- prefix indicates that this is a non-standard or experimental type not officially registered with IANA. While it is widely recognized by development tools and editors, strictly compliant systems might prefer using text/plain for these files.

Can I execute a text/x-asm file directly?

No, files with this MIME type contain source code, not executable machine code. You must process the file using an assembler (such as NASM, MASM, or GAS) to convert the instructions into a binary format that the operating system can run.

What is the difference between .asm and .s files?

Both extensions are served as text/x-asm, but the convention often depends on the operating system or assembler used. Generally, the .s extension is favored on Unix/Linux systems (often with the GNU Assembler), while .asm is common on Windows and with assemblers like NASM.

Are there security risks in serving text/x-asm files?

Serving the file itself is technically safe as it is just text, but exposing source code can reveal proprietary logic or vulnerabilities to attackers. Ensure you do not accidentally expose sensitive system drivers or kernel modules via your web server unless intended for open-source purposes.

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.