internal and external cutomers

I need to identify two contrasting organisations and identify the customers both internal and external of those two organisations. In preparation i should: 1) Draw up a shortlist of two contrasting organisations on which you could base your investigations. State whether they are in the private or puplic sector and in what other respects they are different from each other. 2) Draw up a list of the different types of internal customers of the two organisations 3) Draw up a list of the different types of external customers of the two organisations. Suggestion: Draw up all this data in the form of a table