Flat assembler

Flat Assembler (FASM) - Open-Source x86 Assembly

Fast, flexible, and feature-rich assembler for MS-DOS, Windows, Linux, and macOS - Download now!

What is Flat assembler?

Flat assembler (FASM) is a fast, open-source assembler for the x86 and x86-64 CPU instruction sets. It supports all variations of x86 assembly language syntax and is able to generate optimized binary machine code for all flavors of MS-DOS, Windows, Linux, FreeBSD, Mac OS X/macOS and UEFI firmware.

Some key features of FASM include:

• Very small and fast - the executable itself is under 100KB
• Many directives and syntax options for high-level control over code generation
• Support for macros, loops, conditional assembly and other constructs
• Can assemble code for 16-bit, 32-bit and 64-bit operating systems
• Output formats including EXE, COM, bin, elf, mach-o, coff
• Integrated linker and ability to call external linker (ld)
• Plugin architecture for extending functionality

FASM is commonly used for bootloaders, DOS .com programs, demoscene productions, OS kernels, drivers, and video games. It competes with assemblers like MASM, NASM, YASM and GAS in features but exceeds them in assembly speed and code optimization.

Flat assembler Features

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