In prehistoric pre-computer days, companies kept this information in files or on paper index cards. With the advent of computers, they began to keep this information on computers. However, for years, these databases were simply electronic index cards. You would see a column of customer names, addresses etc. These are known as flat databases.
Index cards are just to small to hold the details of every order.
Besides, the index card was probably kept in some central office. The sales order, invoices, shipping documents etc. were kept in the appropriate departments. Therefore, flat databases have significant limits to their usefulness. About 1970, an IBM scientist wrote a paper that basically created relational databases, which computers make possible. Basically, relational databases link databases together.