Macintosh Classic Overclock Experiment

[360alaska]

I've always wondered if it was possible and despite many comments and opinions to the contrary it is(Kinda). I’ve tried a couple of different crystals but an 18 MHz crystal seems to be the best option, a 20 MHz crystal will allow the machine to boot to SCSI but ADB and SWIM don’t function. Running an 18 MHz crystal runs the CPU @ 9MHZ instead of 7.8 (a 15% increase.)  At 18 MHz ADB and SWIM function however some floppy EMU disk images don’t work. Every actual floppy I’ve tried does work however. Maybe I could give ADB and swim a separate frequency? but that's a lot of work to get to 10mhz....

 

[techknight]

Or you can off-load the CPUs clock to an external crystal and overclock to your hearts content. But, youll still be waiting on the bus. But operations will calculate faster. 

The only thing I dont know, is the 68000 has a synchronous E/VPA/VMA bus for the VIAs, etc and that is also derived from the crystal so we will see...