Monaco is a monospacedsans-seriftypeface designed by Susan Kare and Kris Holmes. It ships with OS X and was already present with all previous versions of the Mac operating system. Characters are distinct, and it is difficult to confuse 0 (figure zero) and O (uppercase O), or 1 (figure one), | (Vertical bar), I (uppercase i) and l (lowercase l). A unique feature of the font is the high curvature of its parentheses as well as the width of its square brackets, the result of these being that an empty pair of parentheses or square brackets will strongly resemble a circle or square, respectively.
Monaco has been released in at least three forms. The original was a bitmapmonospace font that still appears in the ROMs of even New World Macs, and is still the default form in 9 point size even on OS X. The second is the outline form, loosely similar to Lucida Mono and created as a TrueType font for System 6 and 7; this is the standard. There was briefly a third known as MPW, since it was designed to be used with the Macintosh Programmer's Workshop IDE; it was essentially a straight conversion of the bitmap font into an outline font with the addition of some of the same disambiguation features as were added to the TrueType Monaco.