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(web2c.info)Initial and virgin

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Initial and virgin
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  The TeX, Metafont, and MetaPost programs each have two main variants,
called initial and virgin.  As of Web2c 7, one executable suffices for
both variants.

  The initial form is enabled if:
  1. the `-ini' option was specified; or

  2. the program name is `initex' resp. `inimf' resp.  `inimpost'; or

  3. the first line of the main input file is `%&ini';

otherwise, the virgin form is used.

  The "virgin" form is the one generally invoked for production use.
The first thing it does is read a memory dump (Note: Determining the
memory dump to use), and then proceeds on with the main job.

  The "initial" form is generally used only to create memory dumps (see
the next section).  It starts up more slowly than the virgin form,
because it must do lengthy initializations that are encapsulated in the
memory dump file.

  In the past, there was a third form, "preloaded" executables.  This
is no longer recommended or widely used; but see the section below if
you're interested anyway.  In this case, the memory dump file was read
in to the virgin form, a core dump of the running executable was done,
and the `undump' program run to create a new binary.  Nowadays, reading
memory dumps is fast enough that this is generally no longer worth the
cost in disk space and unshared executables.

Preloaded executables