Comment by jonjacky

Here is an emulator of Alto Smalltalk-72 by Dan Ingalls, the original implementor.

http://lively-web.org/users/Dan/ALTO-Smalltalk-72.html

It says that it is emulating the Nova instruction set - the Alto hardware manual at http://bitsavers.informatik.uni-stuttgart.de/pdf/xerox/alto/... says that the standard microcode on the Alto emulated the Nova.