For many years I thought of the difference between a writer and an author as follows: An author is simply one who has written one (or more) book(s). People who are in business may write their accumulated advice into a book, but they are primarily businessmen (or women). Those who have lived through something spectacular may publish their memoirs in a book, but they are not primarily writers. Anyone (literate) can be an author, but not everyone has what it takes to be a writer. To me, one who calls themselves a writer is making a statement of their lifestyle and who they are as a person, which almost certainly includes being an author, whether published or not. This is the way I thought of myself.
In recent months, however, it has come to my attention that there is a common impression among the population that writers are generally unaccomplished, and if they have succeeded in publishing anything that anyone has ever read, it is probably something like a magazine article, an op-ed piece, or a blog post. It is those that call themselves authors that are considered to have more prestige.
It is interesting how these differing impressions and connotations develop, and it leaves me wondering what to call myself, not knowing how people will take it ahead of time. Would it seem too unwieldy and redundant to say I am both?