IA-32 Assembly: Impact of 8-Bit Operations on 32-Bit Registers

During my computer science course, I gave me a binary file and the task of figuring out what it does using reverse engineering techniques (i.e., parse the file and analyze it). I came across one line of IA-32 instruction:

add    %esi,%ecx

      

        
        
        
      

    

I found out that suffixed instructions l

work on 32-bit registers, those with a suffix w

work on 16-bit registers, and I think (but don't know) that non-suffixed operators work on 8-bit registers. Edit: See Ross Ridge's comment which falsifies my assumption.

So my questions are:

• Is my guess above correct?
• If so, what is the effect (as opposed to addl
  
  ) of the instructions above - and what are the effects of other operations such as sub
  
  , mov
  
  etc.?

Thanks in advance!