Most C64 emulators abstract away the electronics and focus on running games. antirez’s c64-hw-sim project takes a lower-level approach by reproducing every chip and connection on an ASSY 250407 Commodore 64 motherboard. Users can remove a chip, connect a pin to ground, or force it high in software. Vintage hardware remains safe.

The simulator can support hardware education and board troubleshooting. A fault reproduced in software can guide checks on a physical board. That only works when the particular failure is covered by the model.

The processor and CIAs receive cycle-accurate emulation. The same applies to SID and VIC-II, using code by Andre Weissflog, also known as flooh. Analog circuitry in the video section is not modeled. Audio and power circuitry are also outside the simulation, so some hardware failures cannot be reproduced.

Even on high-end modern hardware, the simulator runs at about one-third of normal speed. That is sufficient for diagnostics. Games such as Maniac Mansion and Elite are poor targets for it.

Playable emulators are available for personal computers and for platforms including Teensy microcontrollers. Commented source code is available for both the original version of Elite and its C64 port.