[heja2009]

The Apple II was hardwired to run on 60Hz AC and used a limited character set. Minimal hardware design has its downsides. In countries that run 50Hz AC games and other real-time software ran slower or had wrong timing. I noticed quite a number of Apple IIs in Germany being used in engineering or with measurement equipment because of the expansion slots. But software had to be modified to cope for the 50Hz.

[matthewmcg]

Wait, why would the AC frequency affect the CPU clock? Did it use a multiplier instead of an internal clock?

Update: it sounds[1] like other AC circuits might have been affected, perhaps the motors in the disk drive.

[1] "On the hardware side, there were timing differences on the ITT 2020 motherboard, due to the 50 Hz frequency used with the 220 VAC power standards in the UK and Europe." https://apple2history.org/history/ah12/#01

[rbanffy]

I don't think AC is related to a different clock, but the II's system timings are tied to video generation and PAL did 50 fields per second, so maybe that's an issue.

The C64 designed for European markets was slightly slower than its American counterpart.