from: https://en.wikipedia.org/wiki/X86_assembly_language#Examples_2

x86 assembly language has two main syntax branches: Intel syntax and AT&T syntax.[7] Intel syntax is dominant in the DOS and Windows world, and AT&T syntax is dominant in the Unix world, since Unix was created at AT&T Bell Labs.[8]

Many x86 assemblers use Intel syntax, including FASM, MASM, NASM, TASM, and YASM. GAS, which originally used AT&T syntax, has supported both syntaxes since version 2.10 via the .intel_syntax directive.[7][9][10] A quirk in the AT&T syntax for x86 is that x87 operands are reversed, an inherited bug from the original AT&T assembler.[11]

The AT&T syntax is nearly universal to all other architectures with the same mov order; it was originally a syntax for PDP-11 assembly. The Intel syntax is specific to the x86 architecture, and is the one used in the x86 platform’s documentation.