For most of our examples, we don’t use a program called latex but instead one called pdflatex. This is one of a family of related programs, all of which are ‘descendants’ of latex. We have chosen pdflatex because it is perhaps the most widely-used system and directly produces PDF files.
Formats and engines
As described earlier, LaTeX is built on a system called TeX. We call LaTeX a ‘format’: a collection of macros (instructions and commands) that TeX understands. When you run pdflatex, you are actually starting a program called ‘pdfTeX’ with a pre-loaded ‘LaTeX format’. We normally call pdfTeX an engine: a program that understands TeX instructions.
There are three engines in common use today:
- pdfTeX
- XeTeX
- LuaTeX
We will cover XeTeX and LuaTeX later: the main thing we need to know now is that they are capable of loading operating system fonts, whereas pdfTeX can’t do that.
If you are in Japan, or writing lots of Japanese, you might also come across pTeX and upTeX. These are specialized engines for vertical typesetting. LuaTeX can also do a lot of this, but at the moment upTeX, in particular, is still the most popular system for Japanese.