This information was provided by Claris Corporation on 16 March 1998, and incorporated into Apple Computer's Tech Info Library.

Type 1
Type 1 fonts are outline fonts based on the Postscript language. Type 1 fonts are programmed according to the outline font format introduced by Adobe, and the Type 1 format is an open industry standard. Most Postscript printers contain a number of Type 1 fonts in ROM, and additional fonts can be downloaded. Type 1 fonts are more compact than Type 3 fonts, and the Type 1 font is the only font format ATM can rasterize.

Type 1 fonts are both encrypted and hinted. Encryption is the process used to protect font information (hints and character data) from inspection or modification. The encryption key has been published in the Adobe Type 1 Font Format book but is still useful for discouraging casual theft. Hinting consists of information added to an outline font greatly aid in better screen display at small point sizes (when using ATM ) or when printing to low resolution Postscript devices or to non-PostScript devices. Hinting helps control vertical alignment, consistent stem widths, filling-in of counters, and discontinuities in thin strokes.

Type 1 fonts are multi-platform capable (Macintosh, PC, Unix) and more compact than Type 3 or TrueType fonts. They are easier to develop than TrueType fonts and their quality is more consistent. However, most differences between Type 1 and TrueType fonts are transparent to the user. The hand-tuned bitmaps for Windows TrueType fonts look better on screen than the bitmaps ATM creates.

Type 1 fonts are packaged in platform-specific formats (Macintosh, PC, Unix). The printer driver or downloader converts these platform-specific outlines into a device independent format expected by a Postscript printer and specified in the Type I Font Format book. This means a Type 1 font can be downloaded to any Postscript printer and be used by any Postscript file coming from a variety of platforms.

Type 3
Type 3 is an outline font format introduced by Adobe. The Type 3 format is also a Postscript program but unlike the Type 1 format Type 3 fonts do not contain hints. Type 3 fonts are also called "user-defined fonts," and are useful for describing complex graphic shapes, such as a logo. Type 3 fonts, like Type 1 fonts, may be a normal text face or a symbolic font. Unlike Type 1 fonts, the character descriptions for a Type 3 font can potentially use any graphic operator in the Postscript language. Because of this flexibility, the two most common uses of Type 3 fonts are for logos (symbolic) and for bitmap fonts where each character description is a small bitmap (more specifically, an image mask). For example, Microsoft's Windows 3.1 Postscript driver converts TrueType fonts into Type 3 bitmap fonts for printing to Postscript printers. Type 3 fonts are Postscript fonts which do not work with ATM because they allow use of the full Postscript language and ATM is not a full Postscript interpreter. They are not hinted and can exist in bitmap or outline form. They are useful for complex or ornamental fonts or logos. The Faux fonts made by Super ATM are Type 3 fonts.

Other Types
All Postscript fonts, whatever the type, contain the same basic data for describing character shapes. The different types are justdifferent ways of encoding the font for various systems.

Type 0 - Composite, or Kanji fonts. They can handle much larger character sets than Type 1.
Type 1 - Encoded in ASCII, and can be shared across a network.
Type 4 - Encoded in binary format for use on display postscript systems.
Type 5 - These fonts are ROM-based.
Type 6 - These are cartridge based fonts.

Special Characters
Although the Postscript language implements an ASCII character encoding scheme by default, this is changeable. Every font has an array called the Encoding array that maps character codes to names of procedures that draw the characters. It is possible to change this array in order to implement a different encoding system. Getting at unencoded characters is another reason to modify the encoding vector. Many Postscript fonts contain unencoded characters. These characters exist in the font, but by default are not placed in the Encoding array. Older printers containing version I Adobe fonts were delivered with a default "Standard Encoding" that is a subset of the ISO Latin I character set, and were missing characters we currently included see ROM font supplements. All downloadable Adobe fonts, and most ROM fonts depending on their date, are now complete.