Essen Associative Code
The Essen Associative Code (EsAC) is probably the oldest, and certainly the longest-surviving, code for music in active use. Partly because of its longevity, this code forms the basis of hundreds of thousands of analogue (typescript) encodings in European archives. Only a small portion of this material is represented in the computer applications described below.
Origins and History to 1982
Strictly, the term "EsAC" pertains only to work done from 1982 onward. The antecedents of code can be trace back almost 200 years, although most of what survives today dates from after 1860.