The i386 version `as' supports both the original Intel 386 architecture in both 16 and 32-bit mode as well as AMD x86-64 architecture extending the Intel architecture to 64-bits.
| i386-Options | Options |
| i386-Syntax | AT&T Syntax versus Intel Syntax |
| i386-Mnemonics | Instruction Naming |
| i386-Regs | Register Naming |
| i386-Prefixes | Instruction Prefixes |
| i386-Memory | Memory References |
| i386-Jumps | Handling of Jump Instructions |
| i386-Float | Floating Point |
| i386-SIMD | Intel's MMX and AMD's 3DNow! SIMD Operations |
| i386-16bit | Writing 16-bit Code |
| i386-Arch | Specifying an x86 CPU architecture |
| i386-Bugs | AT&T Syntax bugs |
| i386-Notes | Notes |