Wasn't the CPU clock number entirely made up for some time? Afaik on old systems one cycle was one cycle and it lasted as long as frequency implied. Now it's... complicated

The Atari ST ran at 8 MHz. The Amiga ran to nicely sync with the video signal; slightly different numbers for PAL (7.09 MHz) and NTSC (7.16 MHz) systems. But yeah, it used to be you could design a system with rock-solid timing that made an implementation specialized to certain I/O applications cheap and easy... now... not so much