Since June 1998, a cycle-based SID emulator engine is available and is
distributed under the GNU General Public License (GPL). It's called reSID, is
programmed in C++, and so far has been developed by Dag Lem.

Requirement for processor power is huge (don't expect a complex SID emulator
like this to run on a machine with less than 233-300 MHz).

WWW: http://www.geocities.com/SiliconValley/Lakes/5147/resid/