The Apple II used a 6502 CPU clocked at 1.023 MHz which was tightly tied to the NTSC frequency (1/14 of crystal, 3.5 color clocks per CPU cycle). It is well known that the Disk ][ was primarily software driven and thus cycle counting was extremely important since there was no separate micro controller to abstract the mainboard from what the disk controller was doing.
However, there were PAL and SECAM versions of the Apple II as well. When you look at most 8-bit computers of the era, they were also tied to the NTSC clock in some mathematical way and as a result the PAL versions operated a touch slower because of that video standard's 50Hz cycle versus NTSC's 60Hz.
Did the Apple II use a slower clock frequency for the European versions or was the hardware output abstracted so that the computer could run at 1.023MHz and not introduce Disk ][ incompatibility? Heck, was the ASCII $07 beep a different pitch?
If there was a different speed for non-US / NTSC versions, what accommodations needed to be made?