When LaTeX2e was released, personal computers had much less power than nowadays. Moreover, TeX was often compiled with a rather small amount of available memory.
The inclusion of the New Font Selection Scheme (NFSS2), in particular, posed some challenges when LaTeXing big documents. So the developers provided a solution for people with limited memory available: if the autoload option was set during the extraction of
latex.ltx from the sources, not all the kernel was included in the format which was then produced by running
initex on this file: some parts of it were included "on demand", for instance the code for the
Support of the
autoload feature was introduced in the June 1995 release of the LaTeX kernel update and dropped in December 2003.
You can still find a description of this feature in the file
<TEX DIST ROOT>/doc/latex/base/autoload.txt
On some small systems (perhaps most noticeably emTeX for PCs if your
machine is unable to use the TeX386 version) LaTeX uses up a large
amount of the memory available to TeX, leaving very little for storage
of any further commands, complex text (such as tables), floats or
cross references that may occur in a typical document. Note that
these limits are built into the TeX executable and do not directly
correspond to any physical memory that your machine has installed.
In order to help with this problem, we have produced an experimental
configuration of LaTeX in which certain functions are not predefined
in the format, but are loaded automatically from a style file the first
time they are used. This saves a lot of memory in the case that a
document does not use these features.
In this release two environments are ‘auto-loaded’ in this way,
‘picture’ and ‘tabbing’, as are various bits of internal code used in
error handling, font loading and advanced page makeup.