The flat assembler (abbreviated to fasm, intentionally stylized with lowercase letters) is a fast assembler running in a variety of operating systems, in continued development since 1999. It was designed primarily for the assembly of x86 instructions and it supports x86 and x86-64 instructions sets with extensions like MMX, 3DNow!, SSE up to SSE4, AVX, AVX2, XOP, and AVX-512. It can produce output in plain binary, MZ, PE, COFF or ELF format. It includes a powerful but simple macroinstruction system and does multiple passes to optimize the size of instruction codes. The flat assembler is self-hosting and complete source code is included.
The only difference between flat assembler versions included in the following packages is the operating system on which they can be run. For any given source text each version is going to generate exactly the same output file, therefore every one of the following releases can be used to compile programs for any operating system.
Yes. Flat Assembler is free and open-source software released under the Simplified BSD license.
What is the latest version of Flat Assembler?
The latest version is 1.73.32, released on May 22, 2025.
Is it safe to download Flat Assembler?
The download button links to the official installer published on flatassembler.net, the same file Windows Package Manager installs. You can verify the downloaded file by comparing its SHA-256 checksum with d8fe204aab01046ffab3651ef9ff6f1ab72ea907cc2ab2b34fefd774e5814948.
Which Windows versions does Flat Assembler support?
Flat Assembler runs on Windows and is available for 64-bit (x64) systems.
How do I uninstall Flat Assembler?
Open Settings › Apps › Installed apps, find Flat Assembler and select Uninstall. From the command line, run winget uninstall --id=fasm.fasm -e.
Is there a portable version of Flat Assembler?
Yes. Flat Assembler is available as a portable ZIP archive (fasmw17332.zip, 64-bit (x64)) that runs without installation. Copy it to any folder or USB drive and run it from there.
Alternatives to Flat Assembler
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