The Parts of TEX

As I hinted earlier, the name TEX refers not only to a program, but also to a language, and to the typesetting system that they are a part of. A complete system contains some or all of the following pieces:

• The basic program is called virtex. This program knows ``Primitive TEX,'' and is rarely run directly.
• Most systems allow you to type tex to run the virtex program with the ``Plain TEX'' macro package loaded automatically. Similarly, latex runs virtex with the L^ATEX macro package loaded automatically.
• A special program called initex is used to pre-compile macro packages such as L^ATEX so that virtex can load them more quickly. When you first install TEX, you may need to run initex to generate the pre-compiled macro sets, called formats.
• L^ATEX and other macro packages may load other files of macros in the process of typesetting your document. These files are stored in a special directory known as the ``TEX inputs'' directory, and have extensions of sty or tex.
• The result of typesetting your document is a DVI file which specifies what fonts to use, and where to put each letter on the page. In order to print this, you'll need a program which can combine this with the actual font information to generate output for your particular printer.
• Typically, a TEX system uses MetaFont to generate the fonts. This requires that you have virmf and inimf, which function similarly to virtex and initex. You'll also need the MetaFont font description files, typically stored in a ``MetaFont inputs'' directory. Running MetaFont to create a font generates two files. The TFM file contains information about the size of each character, and is used by TEX to typeset your document. Since TFM files are fairly small, it makes sense to keep many of them available. MetaFont also creates a GF file, which contains bitmaps for each character. You can use the gftopk program to convert these into a similar but smaller PK file. Most DVI output programs can handle either PK or GF files. It is possible to use other sources of fonts, such as the fonts built-in to a Postscript printer. This requires TFM files with the correct information for those fonts. Problems with different character numberings are usually resolved through what are called virtual fonts.

There are a lot of pieces, and it can take a while to get everything setup just right, but in typical use, most of this is invisible. You use tex or latex to typeset your document, then run another program to print it out. When you lack a font that you need, you may need to run MetaFont to create it, but after using the system for a while, that happens very infrequently.