<p>The first digit is the number of credit hours.</p>
<p>The second digit indicates course level: 0-1 is intro, 2-7 higher up, and 8-9 is graduate level.</p>
<p>The third digit is more or less meaningless except to indicate sequence (e.g. 301/302).</p>
<p>The lettering is also random, except to indicate sequencing. Sometimes the lettering indicates an alternative version of a class (for engineering majors, for example), but it also happens that the lettering is designated for some purpose, then the purpose changes, but the letter remains as an artifact, making it essentially meaningless.</p>
<p>There’s a longer explanation here: [4</a>. Academic Policies and Procedures | General Information, 2009-2010 | Registrar | University of Texas at Austin](<a href=“http://registrar.utexas.edu/catalogs/gi09-10/ch04/]4”>http://registrar.utexas.edu/catalogs/gi09-10/ch04/)</p>