_(Prolog)'s WAM, an *(abstract VM) to support efficient Prolog compilation.

<A HREF= "http://www.info.ucl.ac.be/people/PVR/implementation.html">"1983-1993: The Wonder Years of Sequential Prolog Implementation"</A>, Peter Van Roy, May/July 1994, Journal of Logic Programming. A survey of implementation technology and systems since the WAM.

Hassan Ait-Kaci published an excellent <A HREF="http://www.isg.sfu.ca/~hak/documents/wam.html">tutorial on the WAM</a> in 1991 ("Warren's Abstract Machine: A Tutorial Reconstruction"). The book is out of print, but its contents are on-line.
