In http://bulkan.upm.edu.ph/~pfalcone/compsci/lang.html,
Intel x86 AT&T (GNU) Assembly Syntax Basics

Operation Suffixes
The data type of the instruction operands are dictated to the assembler by operation suffixes. In AT&T syntax, the following suffixes are supported: 


    Suffix        Data Type
    ------        ---------
       b          byte (8 bits)
       w          word (16-bits)
       l          long (32-bits)
       s          IEEE Single Format (32-bits)
       d          IEEE Double Format (64-bits)

Examples:


       DOS Syntax                     AT&T Syntax
      ------------                   -------------
      
      mov    al,bl                   movb    %bl,%al 
      mov    ax,bx                   movw    %bx,%ax
      mov    eax,ecx                 movl    %ecx,%eax
      mov    eax, DWORD PTR [ebx]    movl    (%ebx),%eax

Use gcc -o movl -ggdb movl.c
to compile code.

Inside gdb
Use disassemble main to show the assembly code of main()
Use x/bx main+n  to display the content of the byte at main+n location

Instruction               Machine Code
movl $0xb, %eax    -->    b8 0b 00
movb $0xb, $al     -->    b0 0b c9