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Differences between Windows and OS/2

This assumption was incorrect; PostScript fonts can be subdivided into two types, one of which observes hard and invariant encodings similar to those that apply to my bitmapped fonts, while the other represents a completely different font mapping strategy. This difference became apparent only when I attempted to share PostScript fonts between Windows and OS/2 and got some unexpected results.

A PostScript font under Windows involves two files, a PFB (PostScript Font Binary) file, which contains the PostScript instructions needed to draw each glyph and some mapping information, and a PFM (Printer Font Metrics) file, which encodes width and kerning information. A PostScript font under OS/2 also uses the same PFB file, but instead of the PFM file it uses an AFM (Adobe Font Metrics) file. The AFM and PFM files contain much of the same basic information (although the AFM file is somewhat more complete); the most important differences are in format (AFM is plain text, PFM is binary) and use (OS/2 uses AFM, Windows uses PFM).

Excerpted from The comp.fonts FAQ, Copyright © 1992-96 by Norman Walsh