Comment by Trouble_007

Two common frequencies used at the introduction of the PC were 3.579545 MHz. & 4.43361875 MHz

Chosen because of the existing supply of cheap xtals manufactured for NTSC & PAL color television sets.

NTSC : https://en.m.wikipedia.org/wiki/NTSC

PAL : https://en.m.wikipedia.org/wiki/PAL

Edits to fix typos :( And add;

Crystal Oscillator Frequencies : https://en.m.wikipedia.org/wiki/Crystal_oscillator_frequenci...