lead lower-case a's in a drawer

There is a very precise reason why the terms “upper” and “lower” case exist. Originally (and still to some traditional type lovers) the two distinctions were called majuscule (upper-case) and miniscule (lower-case).

The terms upper case and lower case originated in the early days of the printing press used with movable type in letterpress printing. The individual type blocks used in hand typesetting are stored in shallow wooden or metal drawers, known as cases, with subdivisions into compartments known as boxes to store each individual letter. In many countries the majuscules and minuscules are stored separately, with a pair of boxes for each typeface at a specific size. For typesetting, the two cases are taken out of the storage rack and placed on a rack on the compositor’s desk. By convention, the case containing the capitals (and small capitals) stands at a steeper angle at the back of the desk, with the case for the small letters, punctuation and spaces, at a shallower angle below it to the front of the desk, hence upper and lower case. The term titlecase refers to the convention, often used in titles and headlines, of an uppercase initial letter followed by lowercase letters in each word. (wikipedia: “letter case”)

Upper and Lower-case Type Drawers

The expression “mind your p’s and q’s” probably comes to us from the tedious and exacting job of sorting metal letters after printing a page and returning them to the type cases. The raised letter on a block of metal type represents a letter that prints in the opposite direction, so a metal p resembles a printed q and vice versa. P’s and q’s were particularly tricky. (source)