This article describes some of the basics of computer font technology and highlights differences between PostScript Type 1, TrueType, and OpenType fonts.
What is a font?
A font (as it applies to computers) is a file or set of files that contain all of the necessary glyphs and positioning information for displaying a particular typeface on a computer display or output device such as a printer.
What is a font family?
A font family is a collection of typefaces; typically they are variations on the same typeface. The Times font family usually consists of a regular face (Times Roman), a bold face (Times Bold), an italic face (Times Italic), and a bold italic face (Times Bold Italic); some font families have many different typefaces and variants.
What is a PostScript Type 1 font?
PostScript is a page-description language that is used to generate images of a formatted page to be sent to an output device. PostScript Type 1 fonts are files that use PostScript to describe the appearance of a typeface; each font requires two files -- a bitmapped or screen font, and an outline font that is used by a PostScript interpreter to generate the final output.
On the Mac OS, a PostScript Type 1 font requires two files; a "font suitcase" of screen fonts, and an PostScript outline font for each screen font in a font suitcase. On Windows, a PostScript Type 1 font is represented by a .pfm file which contains the font metric data, and a .pfb file which contains the data for the characters or glyphs.
What is a Multiple Master font?
Multiple Master fonts are a variation of PostScript Type 1 font; each Multiple Master outline font file contains more than one set of outlines for a typeface, which could be modified on-the-fly to generate variations of a typeface. Multiple Master fonts require a custom utility that could generate one or more instances, which represent a particular configuration of the font.
On the Mac OS, a Multiple Master font is indistinguishable from standard PostScript fonts. On Windows, a Multiple Master font is represented by a .pfm file, a .pfb file, and an .mmm file which contains the data for generating instances for a Multiple Master font. Generating new Multiple Master instances is no longer supported by Mac OS X or Windows, and aspects of the Multiple Master technology have been incorporated into the OpenType font format.
What is a TrueType font?
TrueType fonts are based on an outline font standard developed by Microsoft and Apple as a competitor to PostScript fonts. A TrueType font only requires a single font file to generate both on-screen type and type to be sent to an output device; TrueType fonts are also cross-platform, and can be used on both Mac OS and Windows.
On the Mac OS, a TrueType font may appear as a .ttf file; it can also appear without an extension. In some cases, multiple TrueType fonts can exist in a font suitcase file similar to the suitcase files used for PostScript fonts. On Windows, TrueType fonts always appear as a .ttf file. A .ttf file is required for each typeface in a TrueType family on Windows.
What is a .dfont font?
A .dfont font is a variation on a TrueType font for Mac OS X. Multiple TrueType fonts can exist in a .dfont file; Apple primarily uses it for essential system fonts in Mac OS X. Very few other font developers provide their fonts in a .dfont file.
What is an OpenType font?
OpenType font technology was developed by Adobe and Microsoft as a replacement for both PostScript and TrueType fonts. OpenType fonts can be used on both Mac OS X and Windows computers, and can either contain PostScript-formatted glyph information or TrueType-formatted glyph information; applications such as Suitcase Fusion can determine if an OpenType font is based on PostScript or TrueType, but there is no difference in functionality.
On Mac OS and Windows, an OpenType font appears as an .otf file; an .otf file is required for each typeface. On Windows, OpenType fonts can also appear as a .ttf file.