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:
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 (see section 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.
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