Intel vs AT&T syntax

There're two popular assembly syntaxes: Intel and AT&T. Intel syntax is popular in Windows world. In Linux, AT&T syntax is more popular though GAS (Gnu Assembler) supports both.

The following lists some major differences of the two syntaxes:

1. AT&T prefixes register with % sign
   * Intel:
      eax, ebx, ecx,...
   * AT&T:
      prefix by % sign: %eax, %ebx, %ecx,...
   
   
2. AT&T prefixes immediate value with $ sign, Intel is not
   * Intel: 10, 80h
   * AT&T: $10, $0x80
   
   
3. AT&T and Intel syntax use opposite instruction operands
   * Intel:      mnemonic destination, source 
      Ex:         mov eax, 100
   * AT&T:  mnemonic source, destination
      Ex:        movl $100, %eax
   
   
4. AT&T suffixes instruction to specify instruction's operand size (1 byte: b, 2 bytes: w, 4 bytes: l) but Intel uses directive before operands (1 byte: byte ptr, 2 bytes: word ptr, 4 bytes: dword ptr)
   * Intel:
      mov al, byte ptr foo
   * AT&T:
      movb foo, %al