# Can someone explain what is the 'extended mode'?

During latex compilation with pdflatex+shellescape, the compiler enters:

This is pdfTeX, Version 3.1415926-2.4-1.40.13 (TeX Live 2012) entering extended mode

And stays there for a while, before starting building the pdf output.

• What is it running during that step?
• And is there a way to speed up the process?
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It means that the format is set up to use the etex primitives such as \dimexpr All formats do this by default these days except tex which is set up to not use the extensions and use dvi output so that it is classic plain TeX.

LaTeX always uses this mode (whether or not shell escape is used) see

\$ pdflatex \\relax
This is pdfTeX, Version 3.1415926-2.4-1.40.13 (TeX Live 2012)
restricted \write18 enabled.
entering extended mode

the command

texdoc etex

will show the (quite short) etex manual that explains all the extra primitives, or the source of that will be in your installation somewhere)

etex provides extra registers so you do not run out of count registers it provides infix arithmetic so you can use \dimexpr\textwidth - 1em instead of \advance\dimen@ by 1 em and lots of other small improvements.

Note that these are not "loaded" in any sense they are already compiled in to the program, it is just a binary switch whether to expose them in the document or hide the functionality and act like classic tex. So any startup delay you see is not related to this.

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can you explain why latex enters extended mode only when shell-escape is set (is that even true)? Not-expert here: what are these primitives and what are they used for? (can you link some doc in your answer)? – vrleboss Apr 25 '13 at 9:08
@vrleboss latex always uses etex (for the last 10 years or so) I added some notes to my answer. – David Carlisle Apr 25 '13 at 10:09
I am wondering: I am using a lot of Tikz calculation (intersections of curve in for loop see: tex.stackexchange.com/questions/101141/…) in my latex document. Could that be the reason of the startup delay (not enough registers?). – vrleboss Apr 25 '13 at 12:58
what do you mean by startup, before latex starts showing the list of files loaded? If so it can't be tikz as it hasn't seem that yet:-) – David Carlisle Apr 25 '13 at 13:19
David I tracked down the delay. It comes from \usepackage[pdf,crop=off]{auto-pst-pdf} (necessary in my case: I am using Circuit_macros). Discussion closed :) – vrleboss Apr 25 '13 at 14:07