What are the avaliable font sizes in texlive?

Question

I'm using texlive 2010, and I'm trying to design the layout for a document in plain tex (because I need the document and also I want to learn tex). The input is the following

\font\fifteenrm=cmr15

\font\eighteenbf=cmbx18

\font\twelvebf=cmbx12

\hrule height1mm
\vskip 2mm

{\fifteenrm \noindent Chapter 1}
\vskip 18mm

{\eighteenbf \noindent Analysis I}
\vskip 35mm

{\twelvebf \noindent This is the title}\par

Here is some text...

\bye

the cmr15, cmbx18, and cmbx12 are font files that tex reads and loads but I didn't understand where are those files actually in the system. I looked in the log and found some hints. The log is the following

This is pdfTeX, Version 3.1415926-1.40.11 (Web2C 2010) (format=pdftex 2011.2.24)  24 APR 2012 12:12
entering extended mode
 restricted \write18 enabled.
 %&-line parsing enabled.
**Book.tex
(./Book.tex [1{c:/texlive/2010/texmf-var/fonts/map/pdftex/updmap/pdftex.map}] )
 <c:/Users/Felipe/.texlive2010/texmf-var/fonts/pk/ljfour/public/sauter/cmbx18.6
00pk> <c:/Users/Felipe/.texlive2010/texmf-var/fonts/pk/ljfour/public/sauter/cmr
15.600pk><c:/texlive/2010/texmf-dist/fonts/type1/public/amsfonts/cm/cmbx12.pfb>
<c:/texlive/2010/texmf-dist/fonts/type1/public/amsfonts/cm/cmr10.pfb>
Output written on Book.pdf (1 page, 32853 bytes).
PDF statistics:
 40 PDF objects out of 1000 (max. 8388607)
 18 compressed objects within 1 object stream
 0 named destinations out of 1000 (max. 500000)
 1 words of extra memory for PDF output out of 10000 (max. 10000000)

My question is why is tex looking in two different paths (one is c:/Users/Felipe/... and the other is c:/texlive/2010/...) and how does tex know where it has to search to find an specific font (e.g. cmbx18)?

Answer 1

The original Computer Modern Roman fonts in upright shape (cmr) are designed only at sizes 5, 6, 7, 8, 9, 10, 12 and 17.

However the TeX Live system is able to produce on demand other sizes based on the interpolation scripts by John Sauter. So when you ask for cmr18, the system runs the script and the font is created (a .tfm file and a bitmap for the rendering on screen an on print, the .600pk file).

It would be probably better to ask for

\font\fifteenrm=cmr12 at 15pt

which will scale cmr12 and you'll get a Type1 font for rendering. Similarly for cmbx, which is available at the maximum size of 12pt (in the original form).