This gem shows how you can replace the instruction NOP with "bigger instructions". Assuming we are in a 16-bit segment we can do the following:
2-bytes mov reg,reg ; true NOP
2-bytes xchg ax,ax ; true NOP
3-bytes lea reg,[reg+0] ; true NOP, use 8-bit displacement
The following versions use 32-bit registers and does not work on any CPU less than 80386:4-bytes shl eax,0 ; true NOP
5-bytes shrd eax,eax,0 ; true NOP
6-bytes lea eax,[eax+0] ; true NOP
