What are the differences and similarities between memo and formal letter?

Differences: Memo's are informal instructions or questions usually from a supervisor to a subordinate for information or to have an act performed,or to remind them of something that is coming up and that something needs to be done. A formal letter can be an invitation, a resignation, an instruction to have something done, a letter of dismissal, a reprimand, or even a proposal of marriage. Similarities: They both inform someone of a happening or they instruct someone to do something.